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Risk Assessment of Transformer Fire Protection
in a Typical New Zealand High-Rise Building
By
Anthony Kwok-Lung Ng
Supervised by
Dr Michael Spearpoint
A research thesis presented as partial fulfilment of the requirements for the degree of
Master of Engineering in Fire Engineering
Department of Civil Engineering
University of Canterbury
Christchurch, New Zealand
i
ABSTRACT
Prescriptively, the requirement of fire safety protection systems for distribution substations is
not provided in the compliance document for fire safety to the New Zealand Building Code.
Therefore, the New Zealand Fire Service (NZFS) has proposed a list of fire safety protection
requirements for distribution substations in a letter, dated 10th July 2002. A review by Nyman
[1], has considered the fire safety requirements proposed by the NZFS and discussed the
issues with a number of fire engineers over the last three years. Nyman concerned that one of
the requirements regarding the four hour fire separation between the distribution substation
and the interior spaces of the building may not be necessary when considering the risk
exposure to the building occupants in different situations, such as the involvement of the
sprinkler systems and the use of transformers with a lower fire hazard.
Fire resistance rating (FRR) typically means the time duration for which passive fire
protection system, such as fire barriers, fire walls and other fire rated building elements, can
maintain its integrity, insulation and stability in a standard fire endurance test. Based on the
literature review and discussions with industry experts, it is found that failure of the passive
fire protection system in a real fire exposure could potentially occur earlier than the time
indicated by the fire resistance rating derived from the standard test depending on the
characteristics of the actual fire (heat release rate, fire load density and fire location) and the
characteristics of the fire compartment (its geometric, ventilation conditions, opening
definition, building services and equipment). Hence, it is known that a higher level of fire
safety, such as 4 hour fire rated construction and use of sprinkler system, may significantly
improve the fire risk to health of safety of occupants in the building; however, they could
never eliminate the risk.
This report presents a fire engineering Quantitative Risk Assessment (QRA) on a transformer
fire initiating in a distribution substation inside a high-rise residential and commercial mixed-
use building. It compares the fire safety protection requirements for distribution substations
from the NZFS to other relevant documents worldwide: the regulatory standards in New
ii
Zealand, Australia and United States of America, as well as the non-regulatory guidelines
from other stakeholders, such as electrical engineering organisation, insurance companies and
electricity providers. This report also examines the characteristics of historical data for
transformer fires in distribution substations both in New Zealand and United States of
America buildings. Reliability of active fire safety protection systems, such as smoke
detection systems and sprinkler systems is reviewed in this research.
Based on the data analysis results, a fire risk estimate is determined using an Event Tree
Analysis (ETA) for a total of 14 scenarios with different fire safety designs and transformer
types for a distribution substation in a high-rise residential and commercial mixed-use
building. In Scenario 1 to 10 scenarios, different combinations of fire safety systems are
evaluated with the same type of transformer, Flammable liquid (mineral oil) insulated
transformer. In Scenario 11 to Scenario 14, two particular fire safety designs are selected as a
baseline for the analysis of transformer types. Two types of transformer with a low fire hazard
are used to replace the flammable liquid (mineral oil) insulated transformer in a distribution
substation. These are less flammable liquid (silicone oil) insulated transformers and dry type
(dry air) transformers. The entire fire risk estimate is determined using the software package
@Risk4.5.
The results from the event tree analysis are used in the cost-benefit analysis. The cost-benefit
ratios are measured based on the reduced fire risk exposures to the building occupants, with
respect to the investment costs of the alternative cases, from its respective base case.
The outcomes of the assessment show that the proposed four hour fire separation between the
distribution substations and the interior spaces of the building, when no sprinkler systems are
provided, is not considered to be the most cost-effective alternative to the life safety of
occupants, where the cost-benefit ratio of this scenario is ranked fifth. The most cost-effective
alternative is found to be the scenario with 30 minute fire separation and sprinkler system
installed. In addition to the findings, replacing a flammable liquid insulated transformer with
a less flammable liquid insulated transformer or a dry type transformer is generally
considered to be economical alternatives.
From the QRA analysis, it is concluded that 3 hour fire separation is considered to be
appropriate for distribution substations, containing a flammable liquid insulated transformer
iii
and associated equipment, in non-sprinklered buildings. The fire ratings of the separation
construction can be reduced to 30 minute FRR if sprinkler system is installed. This conclusion
is also in agreement with the requirements of the National Fire Protection Association
(NFPA).
iv
ACKNOWLEDGEMENTS
I would like to take the chance to express my gratitude to all who have put their effort and
support in helping me to complete this research.
Thank you to my supervisor, Michael Spearpoint, for his guidance throughout the
research. I am grateful to him for answering all my queries promptly and with patience.
Thanks to Ove Arup Pty Ltd for the ArupFire Scholarship in 2005.
Thank you to all my lecturers especially Charley Fleischmann, Michael Spearpoint,
Erica Seville, Andy Buchanan and David Purser, who have all helped in the fire
courses and make them both interesting and challenging.
My appreciation to the following persons who provided much technical advice and
significant information to this study:
o Jonathan Nyman for his initiative and advice on the project;
o Wade Enright for his excellent description of the entire transformer system and
good suggestions;
o John Fraser, Vince Duffin, Tim O’Brien, Andre Mierzwa, Shane Watson,
Trevor Buckley, Colin Sydenham and Johannes Dimyadi, for their
involvement and effort in the discussion of transformer fire hazards in
distribution substations and the fire protection systems;
o Pat Hurley for his support in providing the retail prices and the specifications
of transformers and associated equipment;
o Ian Munor for sharing his invaluable experience and knowledge on the ability
of firefighters to control transformer fires.
v
Thank you to the New Zealand Fire Service (April Christensen, Neil Challands, and
Alan Merry) and the National Fire Protection Association (Nacy Schwartz) for
providing me with the invaluable statistical and historical data from their database.
Without this data, I believe the outcome of the research would be invalid and non-
representative.
Thanks to my friends and all fire-mates in 2005 and 2006, for their friendship, help
and laughter. Special thanks to Daniel Ho and Karen Chen for their support and
encouragement.
Thanks to Delwyn Lloydd, Nathaniel Petterson, and Vincent Ho for their excellent
proof-reading skill.
Last but not least, I wish to thank my family for their love and support throughout.
Special thanks to Uncle Frankie Lam for his financial support.
vi
NOMENCLATURE
Abbreviations
NZBC New Zealand Building Code
NZFS New Zealand Fire Service
FIRS Fire Incident Reporting System
NFPA National Fire Protection Association
BCA Building Code of Australia
IEEE Institute of Electrical and Electronics Engineers
EMV Equivalent Monetary Value
QRA Quantitative Risk Analysis
HV/ LV High Voltage/ Low Voltage
AC Alternative current
e.m.f Electromagnetic field
PCB Polychlorinated biphenyl
FHC Fire Hazard Category
FRR Fire Resistance Rating
ETA Event Tree Analysis
FTA Fault Tree Analysis
vii
Definitions
Flash point Minimum temperature of a liquid at which it produces a flammable vapour
Fire point The lowest temperature of a liquid at which it produces a sufficient vapour
that can sustain a continuous flame
Risk
estimate
Process used to assign values to the probability and consequences of a risk as
defined by the international standard organisation ISO [2]
Purpose
group
The classification of spaces within a building according to the activity for
which the spaces are used as defined by the compliance document C/AS1 [3].
Fire hazard
category
The number (grade 1 to grade 4 in order of increasing severity) used to
classify purpose groups or activities having a similar fire hazard, and where
fully development fires are likely to have similar impact on the structural
stability of the building as defined by the compliance document C/AS1 [3].
Firecell
Any space including a group of contiguous spaces on the same or different
levels within a building, which is enclosed by any combination of fire
separations, external walls, roofs, and floors as defined by the compliance
document C/AS1 [3].
Escape
height
The height between the floor level in the firecell being considered and the
floor level of the required final exit which is the greatest vertical distance
above or below that firecell as defined by the compliance document C/AS1
[3].
Distribution
substation
The substation that converts the voltage to a level adapted for household use
(i.e. 415V in 3 phases or 240V in one phase), which contains transformers,
power cables, electrical components and protection devices. In this research,
distribution substation is defined as a substation containing a 750kVA
transformer and the associated electrical equipment in a single room inside a
residential and commercial mixed-use building. Noted that other articles may
use the name of “transformer rooms” or “transformer vaults”. These are
considered to be equivalent to distribution substations.
viii
List of Contents ABSTRACT ............................................................................................................................. i
ACKNOWLEDGEMENTS ...................................................................................................... iv
NOMENCLATURE.................................................................................................................. vi
Abbreviations ......................................................................................................... vi
Definitions ............................................................................................................. vii
LIST OF FIGURES................................................................................................................... xi
LIST OF TABLES .................................................................................................................. xiii
CHAPTER 1 INTRODUCTION .............................................................................................. 1
1.1 Impetus for Research........................................................................................ 1
1.2 Objective of this Research................................................................................ 4
1.3 Scope of this Research ..................................................................................... 5
1.4 Report Outline .................................................................................................. 6
CHAPTER 2 BACKGROUND ................................................................................................ 7
2.1 Electrical Distribution ...................................................................................... 7
2.1.1 Power Generation ................................................................................... 7
2.1.2 Electric Power Transmission .................................................................. 7
2.2 Distribution Substation..................................................................................... 9
2.3 Overview of Transformers ............................................................................. 10
2.3.1 General Construction of Transformers ................................................. 10
2.3.2 Transformer Fundamental Theory ........................................................ 12
2.3.3 Transformer Type ................................................................................. 14
2.3.4 Potential Transformer Problems and Protections ................................. 16
CHAPTER 3 REVIEW OF CODES AND STANDARDS.................................................... 20
3.1 Introduction .................................................................................................... 20
3.2 New Zealand Building Regulations 1992 and Amendments ......................... 21
3.3 New Zealand Fire Service (NZFS) Recommendation ................................... 23
3.4 New Zealand Automatic Fire Sprinkler Standard .......................................... 24
3.5 National Fire Protection Association (NFPA) ............................................... 24
3.6 Building Code of Australia (BCA)................................................................. 28
ix
3.7 Non-Regulation Fire Protection Guidelines for Distribution Substation ....... 29
3.8 Comparison of Transformer Fire Protection Requirements........................... 32
CHAPTER 4 REVIEW OF TRANSFORMER FIRE ............................................................ 35
4.1 Introduction .................................................................................................... 35
4.2 Fire Resistance Rating of Construction.......................................................... 35
4.3 Evacuation in High Rise Building.................................................................. 36
4.4 Study on the Health Effect of Exposure to A Transformer Fire .................... 38
4.4.1 Fitzgerald et al. (1981).......................................................................... 38
4.4.2 Eschenroeder & Faeder (1988) ............................................................. 38
4.5 Experiment on Transformer Oil Fire.............................................................. 40
4.5.1 Heskestad & Dobson (1997)................................................................. 40
4.6 Transformer Ageing ....................................................................................... 41
4.6.1 Bartley (2000, 2002 & 2003)................................................................ 41
4.7 Cost Effective Comparison between Different Types of Transformers......... 43
4.7.1 Goudie & Chatterton (2002) ................................................................. 43
4.8 Studies on the Dielectric Fluids ..................................................................... 44
CHAPTER 5 DATA COLLECTION ..................................................................................... 45
5.1 Statistical Studies ........................................................................................... 45
5.1.1 Sources of Data..................................................................................... 45
5.1.2 Historical Case Study for Transformer Fires........................................ 46
5.1.3 Number of Distribution Substations in New Zealand........................... 48
5.1.4 Fire Incidents Reported to the NZFS FIRS .......................................... 49
5.1.5 Fire Incident Reported to the NFIRS (U.S.) ......................................... 56
5.2 Reliability Data .............................................................................................. 60
5.2.1 Transformer and Associated Equipment............................................... 60
5.2.2 Fire Protection Systems ........................................................................ 61
CHAPTER 6 FAULT TREE ANALYSIS.............................................................................. 65
6.1 Introduction .................................................................................................... 65
6.2 Fault Tree ....................................................................................................... 66
CHAPTER 7 EVENT TREE ANALYSIS ............................................................................. 70
7.1 Introduction .................................................................................................... 70
7.2 Model Overview............................................................................................. 73
7.3 Analysis Approach ......................................................................................... 77
7.4 Identifying the Initiating Event and the Pathway Factors .............................. 79
x
7.5 Structuring the Event Tree Branch Logic ...................................................... 79
7.6 Quantification of the Branch Line Probabilities ............................................ 84
7.6.1 Initiating Event Likelihood................................................................... 84
7.6.2 Smoke Detection System (SDS) ........................................................... 84
7.6.3 Sprinkler System (SS)........................................................................... 86
7.6.4 Manual Fire Service Suppression – Firefighter Action Time (FAT).... 88
7.6.5 Manual Fire Service Suppression – Manual Fire Fighting (MFF) ....... 90
7.6.6 Wall Barrier Integrity Maintained (WBI) ............................................. 92
7.6.7 Summary of the Probability Distributions for the Pathway Factors... 101
7.7 Quantification of the Consequence .............................................................. 105
7.7.1 Introduction......................................................................................... 105
7.7.2 Rate of civilian fatalities and injuries ................................................. 105
7.7.3 Value of statistical life ........................................................................ 108
7.7.4 Consequence of a fire ......................................................................... 109
7.8 Fire Risk Estimation..................................................................................... 110
CHAPTER 8 COST-BENEFIT ANALYSIS ....................................................................... 113
8.1 Introduction to Cost-Benefit Analysis.......................................................... 113
8.2 Methodology ................................................................................................ 115
8.3 Cost Analysis for the Risk Reduction Alternatives...................................... 117
8.3.1 Cost Consideration.............................................................................. 117
8.3.2 Sprinkler System................................................................................. 118
8.3.3 Fire Resistance Rated Constructions (Wall barrier) ........................... 121
8.3.4 Type of Transformer........................................................................... 123
8.3.5 Summary of the Cost Estimate ........................................................... 125
8.4 Risk Reduction Benefit Cost Ratio .............................................................. 126
8.5 Discussion .................................................................................................... 129
CHAPTER 9 CONCLUSIONS AND RECOMMENDATIONS......................................... 132
REFERENCES....................................................................................................................... 136
APPENDIX A: Transformer and Associated Equipment ...................................................... 144
APPENDIX B: Distribution Substation Fire Safety Protection Required by the NZFS........ 151
APPENDIX C: Statistical data of Transformer Fires in Distribution Substations................. 153
APPENDIX D: Calculation of the Probability of Manual Fire Fighting Performance.......... 158
APPENDIX E: Probability Distribution of the Total Risk for each scenario ........................ 159
APPENDIX F: Calculation of the Cost Benefit Ratio ........................................................... 173
xi
LIST OF FIGURES
Figure 2-1: Typical electrical power network 8 Figure 2-2: Schematic drawing of typical transformer 11 Figure 2-3: Fault tree for the transformer fault 18 Figure 4-1: Convective HRR of transformer oil with no drainage, extracted from
Heskestad & Dobson (1997) 40 Figure 4-2: Convective HRR of transformer oil with drainage, extracted from Heskestad &
Dobson (1997) 40 Figure 4-3: Number of transformer failures, reproduced from Bartley 2000 [52] 41 Figure 4-4: Initial cost for transformer dielectric materials, reproduced from Goudie &
Chatterton (2000) 43 Figure 5-1: Number of distribution substations in New Zealand from 1946 to 2006 48 Figure 5-2: Number of distribution substation fires in 2000/06 (Source NZFS FIRS) 50 Figure 5-3: Monthly incidence of distribution substation fires in 2000/06 (Source NZFS
FIRS) 51 Figure 5-4: Hourly trends for distribution substation fires in 2000/06 (Source NZFS FIRS) 51 Figure 5-5: Causes of distribution substation fires (Source NZFS FIRS) 52 Figure 5-6: Object first ignited (Source NZFS FIRS) 53 Figure 5-7: Equipment involved (Source NZFS FIRS) 54 Figure 5-8: Source of ignition (Source NZFS FIRS) 54 Figure 5-9: Extent of flame/ smoke damage (Source NZFS FIRS) 55 Figure 5-10: Number of structure fires originating in switchgear areas or transformer vaults
between 1980 and 2002 (Source NFIRS) 56 Figure 5-11: Civilian injuries as a result of structure fires originating in switchgear areas or
transformer vaults between 1980 and 2002 (Source NFIRS) 58 Figure 5-12: Civilian deaths as a result of structure fires originating in switchgear areas or
transformer vaults between 1980 and 2002 (Source NFIRS) 58 Figure 5-13: Directly property damage as a result of structure fires originating in
switchgear areas or transformer vaults between 1980 and 2002 (Source NFIRS) 59
Figure 5-14: Typical failure rates for various equipment (Extracted from Fig. 11.1 of Moss [30]) 60
Figure 6-1: Fault tree for the transformer fire 68 Figure 6-2: Fault tree for transformer internal overheat 69 Figure 6-3: Fault tree for transformer external overheat 69 Figure 7-1: Structure of the event tree for a transformer fire in a distribution substation 80 Figure 7-2: Probability distribution of the performance of smoke detection systems 85 Figure 7-3: Probability distribution of the performance of sprinkler system 87 Figure 7-4: Probability distribution of FAT – success (PFAT_S) 89 Figure 7-5: Probability distribution of FAT– failure (PFAT_F) 89 Figure 7-6: Probability distribution of equivalent time for transformer with mineral oil 98 Figure 7-7: Probability distribution of equivalent time for transformer with silicone oil 99
xii
Figure 7-8: Probability distribution of equivalent time for transformer with dry type dielectric material 100
Figure 8-1: Basic components of the sprinkler systems in the distribution substation 119 Figure 8-2: Estimated total risk of the alternatives and their corresponding B/C ratio 130
xiii
LIST OF TABLES
Table 3-1: Fire safety precautions from Table 4.1 of the C/AS1............................................23 Table 3-2: NFPA/Wales regulations liquid classification scheme..........................................27 Table 3-3: Summary of the general fire protection requirements for a distribution
substation in a typical residential and commercial mixed-use building .............32 Table 3-4: Summary of the specific fire protection requirements for flammable liquid
insulated transformers in a distribution substation .............................................33 Table 3-5: Summary of the specific fire protection requirements for less flammable
liquid insulated transformers in a distribution substation...................................33 Table 3-6: Summary of the specific fire protection requirements for Askarel/ non-
flammable liquid insulated transformer in a distribution substation ..................34 Table 3-7: Summary of the specific fire protection requirements for dry type transformer
in a distribution substation..................................................................................34 Table 4-1: Properties of transformer dielectric fluid: Typical Values/ Limits........................44 Table 5-1: Life safety consequence of distribution substation fires between 1980 and
2002 reported to the NFIRS................................................................................57 Table 5-2: Failure rate for transformer and associated equipment and some fire
protection systems...............................................................................................61 Table 5-3: Reliability of smoke detection systems .................................................................63 Table 5-4: Reliability of Sprinkler systems.............................................................................64 Table 7-1: Model building characterisation ............................................................................73 Table 7-2: Specifications of the distribution substation..........................................................74 Table 7-3: A brief description of the fire protection systems combination for each
scenario ...............................................................................................................78 Table 7-4: A brief description for each of the 14 outcome events ..........................................81 Table 7-5: Summary of the probability distribution of the performance of smoke
detection systems ................................................................................................85 Table 7-6: Summary of the probability distribution of the performance of sprinkler
system .................................................................................................................87 Table 7-7: Probability that ta_a less or more than 10 minutes..................................................88 Table 7-8: Summary of the probability distribution of firefighters’ action time ....................90 Table 7-9: PMFF in general buildings .......................................................................................90 Table 7-10: Probability distribution of manual fire fighting performance..............................91 Table 7-11: Input parameters and values for determining the fire load density .....................95 Table 7-12: Input parameter and values for determining the ventilation factor......................96 Table 7-13: The input probability distributions for the calculation of equivalent time ..........97 Table 7-14: Summary of the probability distribution of wall barrier integrity maintained
(PWBI) ................................................................................................................100 Table 7-15: Overall summary of the probability distributions for the pathway factors........102 Table 7-16: Rate of casualties in residential apartment and retail areas with various
combinations of fire safety systems..................................................................106 Table 7-17: Rate of casualties per fire in the model building with various combinations
of fire safety systems for each outcome event. .................................................107 Table 7-18: EMV for the life safety consequence of each outcome events ..........................109 Table 7-19: summary of the statistical values of the total risk (NZD$/fire incident) for
each scenario.....................................................................................................111 Table 8-1: Cost of sprinkler systems in the distribution substation ......................................120
xiv
Table 8-2: Initial costs and annual costs of sprinkler systems ..............................................120 Table 8-3: Cost of the FRR constructions.............................................................................121 Table 8-4: Initial costs and annual costs of the FRR construction........................................122 Table 8-5: Cost of different types of transformer .................................................................124 Table 8-6: Initial costs and annual costs of different types of transformers .........................124 Table 8-7: Summary of initial costs and annual costs (Mean value only) ............................125 Table 8-8: A summary of the results of the B/C ratio calculation ........................................127 Table 8-9: Ranking of the B/C ratios with Scenario 1 as the base case................................128 Table 8-10: Ranking of the B/C ratios with Scenario 4 as the base case..............................128 Table 8-11: Ranking of the B/C ratios with Scenario 7 as the base case..............................128 Table 8-12: The ranking for the fire safety design options required in the standards and
guidelines ..........................................................................................................129
1
CHAPTER 1 INTRODUCTION
1.1 Impetus for Research
Nowadays, electricity has become part of our life. Lighting, air conditioning, heating,
computers, phones and cooking appliances, these power consumers can be easily found
around us. According to the annual report 2004/ 2005 by Transpower New Zealand Ltd. [4],
each New Zealand household uses about 8.12kWh per day in average and the power
consumption is increasing each day.
Generally, a 750kVA transformer can support about 60 to130 families or shops depending on
the weather, the season, the number of occupants and the power usage of occupants. Due to
the increasing population and higher loading density in New Zealand each year, more and
more high-rise buildings are built. Typically, a high-rise building containing more than 40
families or shops is likely to have their own transformer installed inside or adjoined to the
building. In this case, the fire safety design of distribution substations may become an
important issue to be addressed for minimising the potential risk to the members of public.
Currently, three types of transformers are commonly used in the market. These include (1) dry
type transformers; (2) less flammable liquid insulated transformers and (3) flammable liquid
insulated transformers. Dry type transformers are transformers containing solid or gas
insulation material. The fire hazard of dry type transformers is generally considered to be low
compared to liquid type transformers due to the limited amount of combustible materials
present in the transformers. For liquid type transformers, less flammable liquid is expected to
have a high fire point (above 300°C) and hence, is more difficult to ignite (Refer to
Section 4.8). From a fire hazard point of view, transformers insulated with flammable liquid
is considered to have the highest fire hazard out of the three types of transformers due to the
combustible liquid oil present and their relatively lower fire point (100°C to 170°C).
2
From the literature, it is understood that transformers are reliable. Failure of transformers as a
result of fire is considered to be very unlikely. However, once transformer fire occurs, the
potential impact on life safety, property and the environment would be very high. This
phenomenon is recognised as a low frequency and high consequence event.
Fire risk is generally measured based on the size of the fire loads in the designated area. In
distribution substations, the fire load density may vary significantly depending on the types of
transformers. For example, distribution substation consists of a dry type transformer is
expected to have low fire load density, including power cables and electrical components, and
hence, the fire risk in the distribution substation is low. On the other hand, when distribution
substation consists of a liquid type transformer, high fire load density is expected due to the
presence of transformer oils. In this case, the fire risk in the distribution substation is
considered to be high. The ranking of different transformer types with respect to the fire risk
is shown in ascending order as follow:
1. Low risk: Distribution substation consists of dry type (e.g. dry air) transformers
and associated electrical equipment
2. High risk: Distribution substation consists of less flammable liquid (e.g.
silicone oil) insulated transformers and associated electrical
equipment
3. Very high risk: Distribution substation consists of flammable liquid (e.g. mineral oil)
insulated transformers and associated electrical equipment
In New Zealand, a compliance document (C/AS1) [3] for fire safety is developed by the
Department of Building and Housing. This compliance document describes solutions for a
wide range of buildings deemed to comply with the New Zealand Building Code (NZBC) [5].
Fire safety design must be accepted by the Building Consent Authority if it satisfies the
provisions of the compliance document. However, the requirements of fire safety protection
systems for distribution substations are not stated in this compliance document. Therefore, the
New Zealand Fire Service (NZFS) has produced a list of fire safety protection requirements
for distribution substations in a letter, dated 10th July 2002. The list of fire safety protection
requirements for distribution substations proposed by the NZFS is shown in Appendix B.
3
A review by Nyman [1], has considered the fire safety requirements proposed by the NZFS
and discussed the issues with a number of fire engineers over the last three years. Nyman has
spoken to the NZFS and he found that the NZFS fire safety requirements for distribution
substations are proposed on the basis of a review of their experience and knowledge
accumulated over the years. However, there has been no significant study conducted in this
fire safety requirement development. Nyman concerned that one of the requirements
regarding the four hour fire separation between the distribution substation and the interior
spaces of the building may not be necessary when considering the risk exposure to the
building occupants in different situations, such as the involvement of the sprinkler systems
and the use of transformers with a lower fire hazard. As a result, the correct approach to the
fire safety design of distribution substations has become a subject of debate between
stakeholders, without agreement on the appropriate level of fire protection for the risk posed
by transformer installation.
Indoor distribution substations are often recommended to be located on the ground level,
providing direct access to outside the building, and to be fire separated from the interior
spaces of the building. Internal access may or may not be provided depending on the site
restriction. The potential hazard of transformer fires to the building occupants is that the fire
and smoke may spread out of the distribution substation through the separation due to
construction failure, improper sealed penetration or leakage through the doorway. Hence, it is
important to control or confine the transformer fire and smoke to the room in order to provide
sufficient time for the building occupants to escape safely without exposing them to any
untenable conditions.
This research conducts a Quantitative Risk Assessment (QRA) of a transformer fire in a
typical New Zealand high-rise residential and commercial mixed-use building when different
fire safety designs and transformer types are applied to the indoor distribution substation. At
the conclusion of the report, a recommendation on the most appropriate fire protection
systems for an indoor distribution substation will be provided as a result of the cost-benefit
analysis. The cost-benefit ratios are measured based on the Equivalent Monetary Value of the
fire risk reduction, with respect to the costs of the combinations of the fire safety systems for
the alternative cases, from its respective base case. Note that in this research the cost-benefit
analysis does not consider property damage, loss of business or environment damage due to
transformer fires and the fire suppression.
4
1.2 Objective of this Research
The primary objective of this research is to evaluate whether the four hour fire separation
between distribution substations and the interior spaces of the building proposed by the NZFS
is a cost-effective solution to safeguard occupants from injury or illness in the event of a
transformer fire in a typical New Zealand high-rise building. The following work statements
were formulated to accomplish this objective:
• Examine and summarise the national and international regulation standards and non-
regulation guidelines for the fire safety design of distribution substations;
• Study the fundamental theory of transformers and the like, such as transformer failure
protection systems, dielectric fields, etc;
• Examine and summarise the characteristics of historical incidents and data for
transformer fires in distribution substations;
• Examine and summarise the reliability of active fire protection systems, such as
sprinkler systems and smoke detection systems;
• Analyses and estimate the transformer fire risks in different scenarios using
Quantitative Risk Analysis, such as Event Tree Analysis;
• Analyses and estimate any cost benefit of the alternative fire safety designs;
• Propose appropriate fire safety designs of distribution substations in a typical New
Zealand high-rise residential and commercial mixed-use building.
5
1.3 Scope of this Research
The scope of this research is to evaluate the feasibility and effectiveness of the proposed fire
safety design solutions to the building occupants’ safety only. Assumptions and limitations
made for this research are illustrated as follow:
General:
• Deflagration and detonation may cause room-boundary failure. However, it is beyond
the scope of this study.
• Property damage, loss of business or environment damage due to transformer fires and
the fire suppression is not a subject of this study.
• Transformers are assumed to be the first item ignited in the distribution substation.
• Where uncertainties are not considered explicitly, conservative assumptions are made.
Source of data :
• Accuracy of data may significantly affect the output of this assessment. Fire incident
data recorded to the Fire Incident Reporting System (FIRS) between 2000 and 2006 is
provided from the NZFS and is used for the assessment in this research. Uncertainty
may be introduced to this data during data collection, manipulation and the application
of the data
• Due to the lack of information on the reliability of sprinkler systems and smoke
detection systems specifically for distribution substations, reliability of sprinkler
systems and smoke detection systems for general buildings has been used instead.
• An appropriately designed sprinkler system should be able to provide early fire
suppression in cases of a fire and reduce the fire size and growth rate. Therefore, this
assessment assumes a transformer fire is to be controlled and confined in the room
once the sprinkler system is activated.
6
1.4 Report Outline
This report consists of eight chapters:
Chapter 2 provides a background study, which includes a brief description of the power
network system and the fundamental theory of transformer systems. It also summarises the
potential failure of transformers and the failure of fire safety protection systems.
Chapter 3 provides a review of the literature with respect to the subject of this research. The
national and international regulation standards and non-regulation guidelines for the fire
safety design of distribution substations are summarised. A review of other relevant articles
and papers is also included in this chapter.
Chapter 4 provides the historical data analysis for distribution substation transformer fires.
This chapter also discusses the reliability of sprinkler systems and smoke detection systems.
Chapter 5 provides a fault tree analysis of transformer fire.
Chapter 6 provides a Quantitative Risk Analysis (QRA) for a transformer fire initiating in a
distribution substation. This includes the methodology of the analysis, event tree analysis and
discussion of the results.
Chapter 7 provides a cost-benefit analysis of the risk reduction alternatives. This includes the
methodology of the analysis, cost-benefit analysis and discussion of the results. The initial
costs and annual costs of sprinkler systems, different types of transformers and the FRR
construction are also provided.
Chapter 8 provides the conclusions and findings of the research. Recommendations and future
work are also discussed.
7
CHAPTER 2 BACKGROUND
2.1 Electrical Distribution
2.1.1 Power Generation
In New Zealand, power is primarily generated from three energy sources. These are (1) Hydro;
(2) Thermal (natural gas and coal fired) and (3) Geothermal power generation. Hydro-power
is the dominant source of electricity generation in New Zealand. Depending on the weather
conditions, typically 60% to 70% of all electricity is produced by hydro power generation,
about 24% by thermal (natural gas and coal fired) stations and the rest by geothermal stations
as mentioned by Contact Energy Ltd. [6], Genesis Energy Ltd. [7] and Meridian Energy Ltd.
[8]. In addition to the power generation, some renewable resources also are used to produce a
small amount of power, such as wind power generation.
2.1.2 Electric Power Transmission
Electric power is normally generated in a power station at 11 to 25kV. In order for the
transmission lines to carry the electricity efficiently over long distances, the low generator
voltage is increased to a higher transmission voltage by a step-up transformer, i.e. 400kV,
220kV or 110kV as necessary. Supported by tall metal towers, lines transporting these
voltages can run into hundreds of kilometres. The grid voltage is then reduced to a sub-
transmission voltage, typically 33kV or 66kV, in terminal stations (known as Power
substations).
8
Sub-transmission lines supply power from terminal stations to large industrial customers and
other lower voltage terminal stations, where the voltage is stepped down to 11kV for load
points through a distribution network lines. Finally, the transmission voltage is reduced to the
level adapted for household use, i.e. 415V (3-phase) or 240V (1-phase) at distribution
substations adjacent to the residential, commercial and small to medium industrial customers.
Figure 2-1 shows a typical electrical network system, in which power is transformed to the
voltages most suitable for the different parts of the system.
Figure 2-1: Typical electrical power network
Power Plants
Step up transformer (Power station)
11~25kV
Long distance transmission 110kV,
220kV or 400kV
Step down transformer (Terminal station)
Medium distance transmission 33kV
or 66kV
Step down transformer (Terminal station)
Short distance transmission 11kV Step down
transformer (Distribution substation)
Large industry
Small to medium industrial customers
Residential customers
Commercial customers
415V (3 phases) or 240V (1 phases)
415V (3 phases) or 240V (1 phases)
415V (3 phases) or 240V (1 phases)
9
2.2 Distribution Substation
Distribution substations are a system of transformers, meters, and control and protection
devices. Although the system design may be different from one to another, the basic principle
for the operation of distribution substations should be similar. In order to control, protect and
monitor the system, there is usually a set of switchgears and meters on both ends of the
transformer which includes a control board, High Voltage (HV) switchgear and Low Voltage
(LV) switchgear. Other equipment, such as lightning arrestors and power cables, will be
placed together within a typical distribution substation.
Depending on site specific constraints, distribution substations may be located outdoor; either
fully exposed or in an enclosure, or in a room inside a building. A transformer fire in a
residential and commercial mixed-use building may potentially expose a larger amount of
people compared to an outdoor transformer fire. Therefore, this research will primarily focus
on a transformer fire in a room inside a building. The regulation standards and non-regulation
guidelines for the fire safety design of distribution substations are discussed in Section 1.1.
10
2.3 Overview of Transformers
2.3.1 General Construction of Transformers
The major components of a transformer are the coils (windings), the core, the tank or casing,
the radiator, and the bushings as shown in Figure 2-2. Generally, transformer coils are made
of copper because it has a lower resistance and is more efficient compared to other metals.
Each winding is wrapped with an insulating material such as paper (the interturn insulation).
The primary winding is usually wound around the transformer core and the secondary
winding is then wound on top of the primary winding. Between each layer of the windings,
another layer of insulating material is wrapped to provide extra insulation between the
windings. (The information in this section is from Lin [9], Gibbs [10], Myers [11], Heathcote
[12] and Zalosh [13]).
The major transformer components are briefly described below:
1) Core is a ferromagnetic material (commonly soft iron or laminated steel) that provides
a path of high magnetic permeability from the primary circuit to the secondary circuit.
2) Windings allow a secondary voltage to be induced in the secondary circuit from the
alternating current (AC) voltage in the primary circuit. The change in magnetic field in
the transformer core caused by applying primary AC voltage causes an induced
magnetic field and, hence, voltage on the secondary winding.
3) Tank or casing, which is usually a reinforced rectangular structure in these
transformers, contains the dielectric material, the core and the windings.
4) Dielectric material is a substance that is a poor conductor of electricity but an efficient
supporter of electrostatic fields. It can be fluid oils, dry solids or gases (see also
section 2.3.3)
5) The expansion tank or conservator containing dry air or dry inert gas is maintained
above the fluid level.
6) Bushing is an insulating structure that provides a conducting path though its centre, its
primary function is to insulate the entrance for an energised conductor into the tank.
11
7) Pressboard barriers, between the coils and between the coils and core, are installed to
increase the dielectric integrity of the transformer.
8) The tap changer is a connection point along a transformer winding that allows the
number of turns to be selected, or so-called voltage regulating device.
9) The radiator provides a heat transfer path to dissipate the internal heat generated in the
transformer.
10) The pressure relief device is used to protect the tank against excessive pressure release
inside a transformer tank. (Refer to Section 2.3.4)
Usually, a nameplate with the transformer details would be attached to a side of the tank. It
helps in identifying the primary coil and the secondary coil ratings, its configuration, volume
of oil and the weight. Photographs of transformer and associated facilities taken from site
visits to two distribution substations in Christchurch, New Zealand are shown in Appendix A.
Figure 2-2: Schematic drawing of typical transformer
Core
Coil Coil Coil
Tap changer
Radiator
Barriers
Dielectric material
Tank or casing
Conservator or Expansion tank
Bushing
Pressure relief device
12
2.3.2 Transformer Fundamental Theory
Transformers are electromagnetic devices that change values of voltage and current without
changing the frequency and the power. By controlling the number of windings, or tapping into
the windings, the output voltage can be adjusted to the design level of voltage.
In a typical transformer, since all fluxes link both coils, the instantaneous induced
electromagnetic fields (e.m.f) and the voltage in the various windings must be directly
proportional to the numbers of turns, hence,
Equation 2-1: 2
1
2
1
||||
NN
VV
≈
where V1 is the primary winding voltage (v)
V2 is the secondary winding voltage (v)
N1 is the number of turns in the primary winding
N2 is the number of turns in the secondary winding
On the other hand, the number of turns between the primary and the secondary windings is
inversely proportional to the current in the various windings; hence,
Equation 2-2: 2
1
1
2
||||
NN
II
≈
where I1 is the primary winding current (A)
I2 is the secondary winding current (A)
As a result of substituting Equation 2-2 into Equation 2-1, an inverse relationship is found
between the voltage ratio and the current ratio.
Equation 2-3: ||||
||||
1
2
2
1
II
VV
≈
13
Connelly [14] states that at normal power frequencies of 25 to 100 cycles, it is necessary to
introduce some factors which may influence the voltage-current relationship. These factors
may be one of the followings:
• The winding resistance – I2R losses in either the primary or secondary coil;
• Energy dissipation from hysteresis and eddy current in the core;
• Leakage inductance;
• Proximity effect and skin effect in windings;
• Electromagnetic radiation; and
• Effects of temperature
The abovementioned factors are the fundamental theory of the voltage and current
transformation. However, transformer operation can be an individual topic. The detail design
of transformers is beyond the scope of this thesis and, therefore, is not provided. The details
on the principle of transformers can be found in Heathcote [12], Connelly [14], Blume [15],
Bean [16] and Mathew [17].
14
2.3.3 Transformer Type
Transformers are designed and built for both indoor and outdoor applications. Depending on
the authority, they are often classified in terms of its power rating or its cooling medium
(dielectric material).
Dielectric material is a poor conductor of electricity. The purpose of using dielectric material
is to insulate the current flow between the wires or the metals, preventing an unwanted
conduction. In this research, a transformer power rating of 750kW is specified for the
assessment. The transformer type is therefore, classified in terms of the dielectric material
type rather than its power rating. Practically, there are four major types of dielectric material
as follows:
• Flammable liquid (such as mineral oil)
• Less flammable liquid (fire point > 300°C, such as silicone oil and vegetable oil)
• Non-flammable liquid (such as Askarels, which is a generic name for Chlorinated
Hydrocarbon insulating liquids)
• Insulating solids and gases (such as dry air)
Josken [18] states that mineral oil is a combustible material and has been the most widely
used fluid for electrical insulation and heat transfer in electrical equipment for more than 100
years. The popularity of mineral transformer oil is due to its availability and its relatively low
cost, as well as being an excellent dielectric and cooling medium. However, Oommen [19]
has found that mineral oil has undesirable characteristics, such as a low fire point (110°C to
185°C), environmental concerns and degradation of insulation paper. Hence, many other
types of dielectric material have been developed as substitutes for mineral oils.
Hallerberg [20] and Mcshane [21] state that during the 1920s, a family of liquids, the so-
called Askarels, were developed to solve the combustibility problem of mineral oil. However,
their use was discontinued in the late 1970s due to the fact that Askarels are commonly
composed of 60% to 70% polychlorinated biphenyls (PCB’s), which are now considered to be
highly toxic and are an environmentally hazardous product. It is also recognised that the
production and commercialisation of PCB’s was officially banned in 1977 by the U.S
15
Environmental Protection Agency (EPA) [22]. As a result, any transformers containing
Askarels have been refilled with other dielectric materials. Bracco [23] reports that some
existing liquid type transformers may still contain PCB’s at various concentrations, usually
less than 10 parts per million (ppm), and hence, these units are often called Askarel insulated
transformers. Some typical trade names for Askarel are as follows (More information of
Askarel (PCB) transformer can be found in Myers [11]).
• Asbestol • Aceclor • Apirolio • Aroclor
• Bakola 131 • Chlorextol • Chlorophon • Diaclor
• Dycanol • Elemex • Eucarel • Hyvol
• Inerteen • Kanechlor • No-flamol • Pyralene
• Pyroclor • Saf-T-Kuhl • Soviol/Sovol/Solvol • Ugilect
Since the use of Askarel is prohibited, other high fire point liquids (also known as less
flammable liquids) have been developed as the replacement fluids, such as polydimethyl-
siloxane (PDMS or silicone oils), polyalphaolefins (PAO), High Molecular Weight
Hydrocarbon (HMWH), Vegetable oil, etc. These dielectric fluids are formulated to withstand
fairly large amounts of electrical arcing and generally have a higher fire or flash point in
comparison to mineral oils. As defined by Technologies [24] and McCormick [25], less
flammable liquids must have a minimum fire point of 300°C. More details about the
properties of transformer dielectric fluids can be found in Section 4.8.
Dry type transformers are transformers where the core and windings are not immersed in an
insulating liquid, but in either an inert gas or solid. Dry type transformers are usually larger
and hotter than the liquid filled transformers with the same power rating. Due to the cost
issues, dry type transformers are more frequently used in distribution substations than the
power or terminal stations. In most gas insulated transformers, Sulfur Hexafluoride (SF6) gas
or dry air, is often used as a cooling medium since it has an excellent dielectric strength,
chemical stability, thermal stability and non-flammability as mentioned in Toda [26].
16
2.3.4 Potential Transformer Problems and Protections
Potential problems
As Gajic [27] stated, 70% to 80% of the total number of transformer failures are due to
internal winding insulation failure. Winding insulation faults may cause a short circuit. Even
if it occurs at a very small point, the energy released at that point can be large within a short
time period. The energy can be large enough to melt the coils and to char or ignite the
insulating material. In such cases, if the protective devices are effective, the damage can be
confined to the object of origin; otherwise, a more serious and costly impact, such as fire and
explosion, may result as mentioned in Hattangadi [28]. The cause of transformer failures can
be classified as one of the following:
• Failure due to defects in internal connections and terminals
• Failure due to interturn insulation in the main windings
• Failure of the main insulation between the windings and the transformer tank
These failures are discussed in detail below:
Failure due to defects in internal connections and terminals:
As a result of bad connections, the contact resistance will be increased. Since the heat
developed in the joint between conductors is directly proportional to the product of the square
of the current and the contact resistance, the temperature of the conductors will also be
increased if this occurs. A circle of increasing temperature and increasing contact power loss
is established. Although there is equipment developed to protect transformers against external
surge voltage, to prevent overloading or to monitor the conditions of the transformer oil, it is
not practicable to detect the local overheating at defective internal connectors and terminals.
When such defects occur, failure of the transformer is almost certain. Hence, the only way of
preventing this failure from occurring is by taking certain precautions in the design,
manufacture and installation of the transformer.
17
Failure due to interturn insulation in the main windings:
Bartley [29] states that interturn insulation faults, such as the paper wrapping, are most likely
as a result of the degradation due to thermal, electrical and mechanical stress or moisture. The
main cause for the interturn insulation failure (insulation breakdown) is due to damage to the
paper insulation or to the loose spacers dropping out. Such defects may occur due to one of
the following reasons:
• Physical damage caused by constant abrasion with the flowing oil and the substances
in the fluid
• Damage caused by thermal damage due to excessive oil temperature
• Degradation of insulation material properties during exposure to moisture (absorbed
from oils)
• Paper insulated conductors that have sharp edges on the corners may get shorted
during service under the effect of vibration, thermal expansion and contraction,
movements caused by electromagnetic force or even the static assembly force between
the coils
Degradation or damage of interturn insulation causes an insulation breakdown between turns
or layers. As a result of insulation breakdown, a high-impedance low-current fault develops in
the windings. At this point, if the protection systems do not quickly detect the fault and isolate
the transformer from the power grid immediately, the fault current will continuously increase
due to decreasing coil impedance and the constant power supply (P = IR2). The high current
will result in an electrical breakdown in the transformer oil and so-called arcing. The arc
decomposes and vaporises the oils and causes the formation of gas bubbles. These gas
bubbles will cause the liquid pressure in the confined tank to increase. If the rate of pressure
increase exceeds the capability of the pressure relief device and other protection devices are
not properly functioning, overpressure may rupture the tank. The escaping gas and liquids
may ignite and fire may result.
18
Failure of the main insulation between the windings and the transformer tank:
There are two main insulation layers between the windings and the transformer tank which
are the mass of the dielectric fluid and the liquid impregnated paper-board laminates. The
failure of the main insulation can be avoided by providing an adequate clearance between the
windings and the transformer tank. Such defects are rare due to the insulation being inspected
during the regular maintenance process and any obstructions or failures can be easily verified
visually.
Hence, a fault tree of transformer failure has been developed as illustrated in Figure 2-3.
Figure 2-3: Fault tree for the transformer fault
OR
Transformer Failure
OR
Failure due to internal connections
and terminals
1.0
Failure due to insulation
breakdown / arcing
2.0
Failure of the main insulation between the windings and the
transformer tank
3.0
OR
Thermal damage
2.2
Insulation properties degradation
2.3 2.4
Manufacture issue
Physical damage
2.1
Used improper connectors
1.1
Over tightened the connectors
1.2
OR gate
19
Furthermore, transformer ageing has not been classified as the cause of failure above.
However, it should be noted that the ageing of the insulation reduces both the mechanical and
dielectric-withstand strength. William H. Bartley, who is a senior member of Institute of
Electrical and Electronics Engineers (IEEE), has been looking into this particular issue since
2000. Some of his published work is reviewed in Section 4.6.1.
Electrical Protections
Transformers are reliable devices which have low electrical failure rates. Moss [30] states that
the failure rate of distribution transformers is 0.02 to 16 failures per 106 operation hours,
which is about 180 x 10-6 to 140 x 10-3 failures per year. However, transformer faults are
considered as a low frequency and high consequence events, explosion and fire may cause
catastrophic damage to property and high numbers of casualties. Depending on the required
level of safety and the economic factors, the level of transformer protection may be varied.
The general electrical devices used to protect against transformer faults are listed below:
1) Circuit breaker or fuses: provides protection for both internal and external faults and
limitation of fault current level
2) Thermal device (thermal relay): monitors the liquid (windings) temperature and
operates when it exceeds a predetermined value
3) Overcurrent relay: operates when there is a short circuit between phases or between
phase and ground.
4) Liquid level gauge: measures the insulating liquid level in the tank
5) Differential relay: operates when the difference between the primary and secondary
side current is over the predetermined value.
6) Lightning arresters: prevents high voltage surges in the system
7) Pressure relief device: reduces excessive pressure created by arcing
8) Sudden pressure relay: operates when it detects the accumulation of pressure in the
tank
9) Gas and oil actuated (Buchholz) relay: operates when it detects the accumulation of
gas in the tank
20
CHAPTER 3 REVIEW OF CODES AND STANDARDS
3.1 Introduction
This chapter studies the prescriptive fire safety solutions for distribution substations in
different countries, such as the acceptable solution (C/AS1) in New Zealand, the Building
Code of Australia (BCA) and the NFPA in U.S. In addition to the safety requirements, non-
regulation guidelines from other stakeholders, such as fire service, electrical engineering
organisation, insurance companies and electricity providers, are also reviewed in this section.
The main purpose of this standards and guidelines review section is to summarise the fire
safety requirements for distribution substations recommended by different authorities and
industries and to compare them with the requirements proposed by the NZFS. It should be
noted that due to the lack of information provided by these stakeholders, the detail studies on
the fundamental concepts and theoretical foundations of these requirements are not provided
in this research.
21
3.2 New Zealand Building Regulations 1992 and Amendments
As the regulatory objective, all buildings in New Zealand must comply with the New Zealand
Building Code (NZBC), which is a schedule to the Building Regulations 1992 and the
subsequent amendments [5]. The NZBC is a performance based code which has mandatory
provisions to comply with The Building Act 2004. Out of the 37 performance clauses in the
Building Regulations, there are four relevant clauses to the fire safety in buildings. These are:
C1 - “Outbreak of Fire”,
C2 – “Means of Escape”,
C3 – “Spread of Fire” and
C4 – “Structural Stability during Fire”.
A compliance document (C/AS1) [3] is developed by the Department of Building and
Housing. It is one way to satisfy the performance requirements of the NZBC. However, the
fire safety design of distribution substations is not clearly specified in the C/AS1. Relevant
clauses to the model building as defined in Section 7.2 are discussed below:
Purpose groups and Fire Hazard Category (FHC)
Residential apartment, which is a space for sleeping, is defined as being purpose group SR
and the FHC is one as per Table 2.1 of the C/AS1. Retail shop, which is a space for selling
goods, is defined as being purpose group CM and the FHC is two as per Table 2.1 of the
C/AS1.
Vector Ltd [31] states that distribution substations shall be considered as a space for providing
intermittently used support functions, known as purpose group ID within the C/AS1.
According to the Fire Engineering Design Guide [32], a typical power station and transformer
winding occupancy has a fire load of 600MJ/m2. This fire load density is equivalent to FHC
of two as described in the C/AS1 Clause 2.1.3.
Fire safety precautions
The relevant clauses of the C/AS1 are listed below:
22
Clause 4.5.11– “Where any upper floor contains a sleeping purpose group, all floors below
shall have an appropriate alarm system which shall activate alerting devices in all sleeping
areas within the building. …For SR purpose group where any lower floor contains a purpose
group other than SR, all lower floors shall have heat or smoke detectors or sprinklers (Types
3, 4 or 6).” (See below for descriptions of the fire safety precautions types)
Clause 6.2.1 – “Where adjacent firecells on the same floor level are permitted by Table 4.1 to
have a F rating of F0, they shall be fire separated from one another. The fire separations
shall have a FRR of no less than that required by Part 6 or Part 7 (for a specific purpose
group or situation), or 30/30/30, whichever is the greater.”
Clause 6.8.1 – “Purpose Groups SR – Every household unit in purpose group SR shall be a
single firecell separated from every other firecell by fire separations having a FRR derived
from the F rating in Table 4.1/5, or 30/30/30, whichever is the greater.”
Clauses 6.11.1 –“Firecells in which ID is the primary purpose group, shall meet the same fire
safety precautions as specified in Table 4.1 for purpose group WM, and shall be separated
from adjacent firecells by fire separations having a FRR of no less than 60/60/60.” (Purpose
group WM is a spaces used for working business or storage with medium fire load and
slow/medium/fast fire growth rates).
Clause 6.11.4 –“Where plant is contained in a building separated by 3.0 m or more from any
adjacent building, only Paragraph 6.11.3 c) shall apply.”
Clause 6.11.3 (c) –“Its floor level no lower than the ground level outside the external wall if
gas is the energy source.” (It should be noted that substation is a plant room but the
flammable liquid is not used as an energy source. Hence, Clause 6.11.3 (a) and (b) is not
applicable.)
Depending on the purpose group, the FHC, the escape height and the occupant load, the fire
safety precautions for the firecell can be found from Table 4.1 of the C/AS1. Table 3-1 shows
the fire safety precautions for purpose group SR, CM and WM (the same fire safety
precautions are required for purpose group ID as per Clause 6.11.1 of the C/AS1).
23
Table 3-1: Fire safety precautions from Table 4.1 of the C/AS1 Firecell Residential apartment levels Retail shops Distribution substation
Purpose group SR CM WM (ID) FHC 1 2 2
Escape height 10m - 25m 0m 0m Occupant load Less than 40 occupants Less than 100 occupants Less than 100 occupants
FRR of 45/45/45 (Table 4.1/5 & Clause 6.8.1)
FRR of 30/30/30 (Table 4.1/1 & Clause 6.2.1)
FRR of 60/60/60 (Clause 6.11.1)
Type 4 (Table 4.1/5) Type 3, 4 or 6 (Clause 4.5.11)
Type 3, 4 or 6 (Clause 4.5.11)
Type 14 (Table 4.1/5) Type 2 (Table 4.1/1) Type 3 (Table 4.1/1) Type 16 (Table 4.1/5) Type 18 (Table 4.1/1) Type 16 (Table 4.1/1)
Fire Safety Precaution
Type 18 (Table 4.1/5) Type 18 (Table 4.1/1) Where Type 2 = Manual fire alarm system Type 3 = Automatic fire alarm system with heat detectors and manual call point Type 4 = Automatic fire alarm system with smoke detectors and manual call point Type 6 = Automatic fire sprinkler system with manual call point Type 14 = Fire hose reel Type 16 = Emergency lighting in exitways Type 18 = Fire hydrant system
3.3 New Zealand Fire Service (NZFS) Recommendation
An interpretation of distribution substation fire protection requirements was made by the
NZFS in a letter, dated 10th July 2002. This letter is reproduced in Appendix B. Issue two
states that the construction separation between the distribution substation and the interior
spaces of the building, including ceiling and floor, shall have FRR construction of no less
than four hours. It goes on to state that distribution substations, the exterior access shall have
a minimum clear opening area of 800 x 2100mm wherever possible and that if the building is
a non-sprinklered building, no sprinkler system is required in the distribution substation but
heat detectors are recommended.
24
3.4 New Zealand Automatic Fire Sprinkler Standard
New Zealand Automatic Fire Sprinkler Standard NZS 4541:2003 [33] is the standard for the
installation of sprinkler systems in New Zealand. As specified in Clause 203.5.2, sprinkler
systems are required for liquid type transformers within building. For liquid type transformers,
sprinkler systems are required to provide a design density of discharge of at least 10 mm/min
over all transformer surfaces. From Table 2.1 of NZS 4541:2003, dry type transformers may
fall into an ordinary hazard group one or two (OH1 & OH2) based upon an occupancy
classification of either industrial or commercial plant rooms or electricity generation and
distribution. The required sprinkler systems design density of discharge for dry type
transformer is 5mm/min at minimum.
3.5 National Fire Protection Association (NFPA)
The National Fire Protection Association (NFPA) is an international organisation (U.S. based)
established in 1895. It has developed a series of recommendations or standards providing
design advice on fire, electrical and life safety to the public. The recommendations, codes and
standards produced by the NFPA that may apply to transformer fire protection and associated
electrical facilities are shown below:
• NFPA 70, National Electrical Code (NEC): Article 450-Transformers and Transformer
Vaults 2005 Edition
• NFPA 850, Recommended Practice for Fire Protection for Electric Generating Plants
and High Voltage Direct Current Converter Stations 2005 Edition
• NFPA 13, Standard for the Installation of Sprinkler systems 2002 Edition
• NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection 2001 Edition
• NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Bases Fire
Protection System 2002 Edition
• NFPA 30, Flammable and Combustible Liquids Code 2003 Edition
• NFPA 220, Standard on Types of Building Construction 2006 Edition
25
NFPA 70 National Electrical Code (NEC) [34]
The National Electrical Code (NEC) is a safety standard for the installation process of
electrical systems. The fire safety design for different types of transformers, such as dry type,
less flammable liquid insulated, non-flammable liquid insulated, Askarel insulated and oil
insulated transformer, are covered in Article 450. The relevant clauses in relation to
distribution substations are extracted from this standard and re-written as follow:
Clause 450-21 b) & c) Dry type transformers installed indoors
Individual dry type transformer of more than 112.5kVA shall be installed in a transformer
room (distribution substation) of fire resistant construction with a minimum FRR of 1 hour.
For dry type transformer up to 35,000 volts, no transformer vault is required, where the
characteristic of the transformer vault are specified in part 3 of Article 450.
Transformer Vault: Part 3 of Article 450 states that the minimum fire resistance for the
transformer vault construction, such as walls, roof, floor and doorway, should have a FRR of
no less than 3 hour or it can be reduced to 1 hour FRR if an automatic sprinkler suppression
system, water spray, carbon dioxide or halon, is installed. In addition to the requirements,
only qualified persons are allowed to access the transformer vault. Ventilation systems are
required in this case, in which an automatic closing fire damper shall also be included. If
natural ventilation is used, the combined net area of all ventilating openings shall be not less
than 1900mm2 per kVA of transformer capacity in service (1.425m2 for a 750kVA
transformer). Practically, a concrete wall with overall thickness of 211mm and 311mm shall
have 3-hour and 4-hour fire resistance, respectively. Note that transformer vault in the NEC
may imply they are distribution substations as defined in this research.
Clause 450-23) Less flammable liquid insulated transformers installed indoors:
If the transformer is up to 35,000 volts, no transformer vault is required. Indoor installations
shall be permitted with one of the following cases: (Note that less flammable liquid means the
liquid has a fire point of not less than 300°C)
26
Case 1: • In Type I and Type II buildings
o As stated in Clause 4.3 of NFPA 220 [35], both Type I and
Type II building structural components are non-combustible or
limited combustible materials. The difference between Type I
and Type 2 building is that the entire construction of Type I
building must have fire rating of no less than 90 minutes
except the interior and exterior non-load bearing walls, while
Type II construction may not have any FRR construction.
• In areas which no combustible materials are stored;
• Provided a liquid confinement area;
Case 2: • Provided with an automatic fire extinguishing system
• Provided a liquid confinement area
Case 3: • In accordance with Clause 450.26 as described below (Installed in a
transformer vault).
Clause 450-24) Non-flammable liquid insulated transformers installed indoors:
If the transformer is up to 35,000 volt, no transformer vault is required but a liquid
confinement area and a pressure relief vent shall be provided.
Clause 450-25) Askarel insulated (PCB contaminated) transformers installed indoors:
If the transformer is up to 35,000 volt, no transformer vault is required. Pressure relief vent
should be provided for transformer rated over 25kVA.
Clause 450-26) Oil insulated transformers installed indoors
This type of transformers should be installed in a transformer vault.
27
NFPA 850 Recommended Practice for Fire Protection for Electric Generating Plants and High
Voltage Direct Current Converter Stations [36]
Clause 5.2.5 of the NFPA 850 states the design criteria regarding the fire protection systems
for distribution substations. These recommendations are in relation to Clauses 450-26 of
NFPA 70. For oil insulated transformers containing more than 379 L of oil, a construction
having a FRR of no less than 3 hour shall be used for the transformer vaults or it can be
reduced to 1 hour FRR if a sprinkler system is installed.
Dry type transformers are suggested for indoor installations under this document. Openings in
fire barriers are mentioned in Clause 5.2.2, it states that “All openings in fire barriers should
be provided with fire door assemblies, fire dampers, through penetration seals (fire stops), or
other approved means having a fire protection rating consistent with the designated fire
resistance rating of the barrier…”. Moreover, in an area containing switchgears and relays,
smoke detectors are required under Clause 7.8.4.
NFPA 30 Flammable and Combustible Liquids Code [37]
According to Clause 3.3.25 of NFPA 30, liquids can be classified based on their flash points
as shown in Table 3-2. Additionally, the liquid classification scheme from the Hazardous
Waste (Wales) Regulations 2005 [38] is also included in the table for comparative purpose.
Note that typical mineral oil have the lowest flash point at 100°C; it is therefore considered as
a Class III combustible liquid.
Table 3-2: NFPA/Wales regulations liquid classification scheme Liquid classification Flash point range
NFPA - Class I Flammable liquid < 37.8°C
NFPA - Class II Combustible liquid > 37.8°C and < 60°C
NFPA - Class III Combustible liquid > 60°C
Wales regulation Highly Flammable liquid < 21°C
Wales regulation Flammable liquid > 21°C and < 55°C
28
NFPA 13 The Installation of Sprinkler systems [39] / NFPA 15 Water Spray Fixed Systems
for Fire Protection [40] / NFPA 25 Inspection, Testing and Maintenance of Water-Bases Fire
Protection System [41]
According to Clause 5.4 and Clause 13.31.1 of NFPA 13, distribution substations shall be
categorised as Extra Hazard Group 2 occupancy. For a mineral oil insulated transformer,
automatic sprinkler suppression systems with discharge density of 10.2mm/min covering area
up to 325m2 are required. The installation of nozzles is required in NFPA 15 to cover areas
where spills may travel or accumulate. NFPA 25 provides detailed criteria to be followed
when fire protection systems are damaged.
3.6 Building Code of Australia (BCA)
The BCA is a prescriptive standard in Australia. In clause C.2.13 (a) and (b) of the BCA, an
electricity substation and a main switchboard located within a building (known as an
distribution substation in this research) must –
(i) be separated from any other part of the building by construction having a fire
resistance level of not less than 120/120/120 and;
(ii) have any doorway in that construction protected with a self-closing fire door
having a fire resistance level of not less than -/120/30.
In the Building Code of Australia, the fire safety precaution is dependent on the type of
building, and the escape height and floor area of the compartment. In cases where distribution
substation is installed in a high-rise residential and commercial mixed-use building having an
escape height of less than 25m and the floor area of less than 2,000m2, an automatic smoke
detection and alarm systems and sprinkler systems are required.
29
3.7 Non-Regulation Fire Protection Guidelines for Distribution Substation
Many stakeholders, such as electrical engineering organisation, insurance companies and
electricity providers, have developed their own guidelines applicable to the fire protection of
distribution substations. These guidelines have been widely used by many industries as
references to select the fire protection systems for distribution substations. Four guidelines are
examined in this research. Note that as required by the electricity providers for commercial
purposes, the names of the companies are not given in this research.
Institute of Electrical and Electronics Engineers (IEEE)
IEEE is an international organization that develops standards for electronic and electrical
technologies. An IEEE standard, IEEE 979-1994[42], related to substation fire protection is
examined. IEEE 979-1994 is a revision of IEEE 979-1984. The title of the standard is “IEEE
Guide for Substation Fire Protection”, in which the fire protection for distribution substations
is described in Clause 9.1 through Clause 9.6.
In this guideline, low smoke cables are recommended for use in distribution substations.
Unless installed cables comply with the flame test parameters specified in IEEE Standard
383-1974 and are properly sealed to the fire rated barriers, the cables shall be installed in trays
or trenches cast with removable metal or fire-retardant material coverings. As stated in
Clause 9.3, the use of oil filled equipment inside a building is not recommended. If it is used,
it shall be installed in transformer rooms (distribution substations) or vaults constructed with a
fire rating sufficient to withstand the largest possible fire that may occur, and a minimum of
two exits is expected. However, the fire ratings for transformer vault construction are not
provided in this standard. In addition to the fire safety protection system, fixed fire
extinguishing systems and oil containment are recommended in this standard.
30
Factory Mutual Insurance Company (FM Global):
FM Global is a U.S. based insurance company, which provides property insurance protection
for commercial and industrial risk and risk management services. One of their datasheets, FM
Global Property Loss Prevention Datasheet 5-4 (2005), provides the fire protection guidelines
for substations. FM Global is known as a Highly Protected Risk (HPR) insurer; their design
criteria have been established not only to the fire exposure of a transformer, but also the
potential damage to the transformer and the possible business interruption effects that a
transformer fire can cause. Some loss histories are also covered in the datasheet.
As recommended in the datasheet, indoor transformers shall have a minimum of 0.9 m
separation from the building walls. Smoke detection and fire alarm systems that are connected
to the Fire Service and the electrical providers shall be installed in distribution substations. An
appropriately designed mechanical ventilation system is also required. More specifically, the
datasheet also provides the specific fire protection requirements for different types of
transformers installed, which are listed as follow:
For oil insulated transformers containing more than 378.5 litres of oil, the transformer rooms
(distribution substations) shall have at least one external wall and the constructions shall be
fire rated with a minimum of 3 hour FRR or it can be reduced to 1 hour FRR if an automatic
sprinkler system with discharge density of 15 mm/min over the room area is installed.
For less flammable liquid insulated transformers, the transformer room (distribution
substation) shall be constructed with a minimum of 1 hour FRR or sprinkler systems with a
discharge density of 10 mm/min over the transformer room (distribution substation) is
required to be installed.
For dry type transformers, there are no specific fire protection requirements more than
keeping the transformers away from other combustible materials by a non-combustible barrier
or a distance of 1.5 m horizontally and 3 m vertically. However, air-cooled transformers are
recommended to be in a pressurised room when they are exposed to dusty or corrosive
atmospheres.
31
Askarel insulated transformers containing more than 50 ppm PCB’s are not allowed under
this organisation; hence, a liquid replacement is required when the PCB concentration is more
than 50 ppm. Furthermore, four additional requirements are prescribed for the Askarel
insulated transformer rooms, which include (1) the installation of oil containment, (2) keeping
the room free of combustibles, (3) properly seal the wall penetrations and (4) exhausting air
directly to the outside.
Electricity provider (1):
This organisation is one of the largest electricity network management companies in the
South Island of New Zealand. The fire protection requirements for distribution substations are
found in one of their electricity network design standards produced in 2001. This guideline
recommended distribution substations to be located at ground level with at least one wall is an
external wall. When liquid type transformers are used in the building, it shall be installed in a
vault constructed with a minimum of 2 hour FRR. Any openings and penetrations within the
FRR barrier shall be properly sealed or an automatic closing damper shall be provided.
Ventilation systems are also recommended. If natural ventilation is used, the combined net
area of all ventilating openings shall be not less than 2000mm2 per kVA of transformer
capacity in service (1.5m2 for a 750kVA transformer). If mechanical ventilation is used, the
airflow rate at 40m3/min per transformer is required.
Electricity provider (2):
This organisation is another electricity network company in New Zealand but their major
customers are in the North Island. They created a fire protection guideline for distribution
substations in 1997. Their fire protection requirements are based on the Electricity
Regulations 1997 and the Building Act 1991. As recommended in this guideline, the fire load
density in a distribution substation shall be considered to contain a total of 3500MJ/m2 with
FHC of 4. It is recommended that the distribution substation should be constructed with a
minimum of 2 hour FRR or it can be reduced to 1 hour FRR if sprinkler system is installed.
32
3.8 Comparison of Transformer Fire Protection Requirements
A summary of fire protection requirements for distribution substations in typical residential and commercial mixed-use buildings from the above
standards and guidelines is illustrated in Table 3-3 through to Table 3-7:
Table 3-3: Summary of the general fire protection requirements for a distribution substation in a typical residential and commercial mixed-use building Fire protection requirements C/AS 1 NZFS NFPA BCA IEEE FM Global Electricity
provider (1) Electricity
provider (2)
Detection system Heat/ Smoke detector
Heat detector
Smoke detector
Smoke detector
Heat/ smoke detector
Smoke detectors
Smoke detectors Not Spec.
Sprinkler system See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
FRR construction See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
See tables below
Smoke management system 1 Not Spec. Not Spec. Req. Not Spec. Req. Req. Req. Not Spec.
- Natural venting (Venting openings)
>1.425 m2 >1.5 m2
- Mechanical venting (Airflow rate)
Not Spec. >40 m3/min
- Auto closing damper
N/A N/A
Req.
N/A Not Spec. Not Spec.
Req.
N/A
Location of distribution substation (on an external wall) Not Spec. Rec. Rec. Not Spec. Not Spec. Rec. Rec. Rec.
Oil containment 2 Not Spec. Rec. Rec. Not Spec. Rec. Rec. Rec. Not Spec. 1 Either natural venting or forced venting is installed 2 For liquid type transformer only
Where Spec. = specified; Req. = required; Rec. = recommended; N/A = Not Applicable
33
Table 3-4: Summary of the specific fire protection requirements for flammable liquid insulated transformers in a distribution substation Specific requirements for flammable liquid insulated
transformers 1 C/AS 1 NZFS NFPA BCA IEEE FM Global Electricity
provider (1)Electricity
provider (2)
Option 1: Provide FRR construction and no sprinkler system
FRR construction 1 hour 4 hour 3 hour Not Spec. Not Spec. 3 hour 2 hour 2 hour
Option 2: Allow the reduction to FRR construction by providing sprinkler system
FRR construction 1 hour 2 hour 1 hour 1 hour
Sprinkler system (Discharge density) Not Spec. Not Spec.
Req. (10.2 mm/min)
Req. (Not Spec.)
Not Spec. Req.
(15 mm/min)
Not Spec. Req.
(Not Spec.) 1 Two alternative fire safety designs to meet the standards and guidelines when a flammable liquid insulated transformer is installed.
Table 3-5: Summary of the specific fire protection requirements for less flammable liquid insulated transformers in a distribution substation Specific requirement for less
flammable liquid insulated transformers 2
C/AS 1 NZFS NFPA BCA IEEE FM Global Electricity provider (1)
Electricity provider (2)
Option 1: Provide FRR construction and no sprinkler system
FRR construction Not Spec. Not Spec. 3 hour Not Spec. Not Spec. 1 hour Not Spec. Not Spec.
Option 2: Allow the reduction to FRR construction by providing sprinkler system
FRR construction 1 hour No FRR req.
Sprinkler system (Discharge density) Not Spec. Not Spec.
Req. (Not spec.)
Not Spec. Not Spec. Req.
(10 mm/min)
Not Spec. Not Spec.
2 Two alternative fire safety designs to meet the standards and guidelines when a less flammable liquid insulated transformer is installed.
Where Spec. = specified; Req. = required;
34
Table 3-6: Summary of the specific fire protection requirements for Askarel/ non-flammable liquid insulated transformer in a distribution substation Specific requirement for
Askarel/ non-flammable liquid insulated transformers
C/AS 1 NZFS NFPA BCA IEEE FM Global Electricity provider (1)
Electricity provider (2)
FRR construction Not Spec. Not Spec. No FRR req. Not Spec. Not Spec. No FRR req. Not Spec. Not Spec.
Table 3-7: Summary of the specific fire protection requirements for dry type transformer in a distribution substation Specific requirement for dry
type transformers C/AS 1 NZFS NFPA BCA IEEE FM Global Electricity provider (1)
Electricity provider (2)
FRR construction Not Spec. Not Spec. 1 hour Not Spec. Not Spec. No FRR req. Not Spec. Not Spec.
Where Spec. = specified; Req. = required;
35
CHAPTER 4 REVIEW OF TRANSFORMER FIRE
4.1 Introduction In this chapter, several literature sources have been reviewed in relation to transformer fires,
the health effect of a transformer fire, the fire resistance rating of construction, evacuation
from high rise buildings during a fire, characteristics of transformer fires and the properties of
the major combustible material in transformer i.e. dielectric material. Other informative
studies, such as transformer ageing and cost comparison between different types of
transformer are also reviewed to provide background information for the cost benefit
assessment.
This chapter does not provide the literature review on the specific factors and parameters used
in the risk assessment i.e. event tree analysis and cost-benefit analysis. These reviews are to
be provided in the relevant sections in Chapter 7 and Chapter 8.
4.2 Fire Resistance Rating of Construction
At the Building and Research Association of New Zealand (BRANZ), the fire resistance time
of building elements is commonly determined by the ASTM or NFPA fire endurance test
using the standard ISO fire curve as described in Australia standard AS1530.4-2005, which is
similar to ISO 834 or British Standard BS 476 part 20-22 and ASTM E119, to provide a fire
rating. However, research has been performed to study the behaviour of structures in the case
of ISO fire exposure and a real fire exposure. It is found that the actual fire resistance time of
building elements exposed to real fire conditions could have significantly different times from
the fire rating derived from standard tests, depending on the characteristics of real fire, such as
fire growth rate, fire load density, location of fire, and the geometry of the fire compartment,
such as compartment size, ventilation conditions, opening definition, glass breaking.
Nyman [43] has recently studied the equivalent FRR of construction elements exposed to
realistic fires. In the research, three full-scale compartment tests were experienced,
establishing the actual times to failure of construction with real fire exposure, and compared
the results with the fire resistance rating of the construction derived from standard tests. The
36
outcome of the research shows that standard fire test method with ISO fire curve is considered
not conservative for use on load-bearing building elements. It has found that real fire
exposure can be more severe than the AS1530.4 standard furnace test exposure. It can grow
quicker than standard ISO fire, increase the compartment temperature in the fire growth phase
and cause the failure of building elements, such as integrity, insulation and stability, to occur
earlier than the fire resistance rating. In the conclusion, it stated that the failure times of the
test assemblies in the compartment tests confirms that construction exposed to realistic fires
will fail at times significantly less than the FRR derived from standard tests, for fires which
are more severe than the standard test fire exposure.
A fire curve for Hydrocarbon heating regime, which has a more rapid fire growth in the
earlier stage, is introduced in the AS1530.4-2005 standard for measuring the FRR. This fire
curve can predict the FRR construction in a more severe fire environment. However, since the
use of alternative heating regime is optional in accordance with Appendix B of the AS1530.4-
2005 standard, fire curve for Hydrocarbon heating regime is not commonly used.
4.3 Evacuation in High Rise Building
In a high rise building occupied with residential and commercial space, the evacuation time of
the occupants could potentially take more than couple hours to evacuate the building.
Technically, the required safe egress time (RSET) is defined as the time required for
evacuation of occupants to a place of safety. As stated in the fire engineering design guide
[32], the RSET can be determined by sum of fire detection time, pre-movement time, travel
time and queue time. In residential buildings, occupants may or may not be alert, awake and
familiar with the building fit-out and the location of exits (e.g. new tenants or guests). As the
result, the RSET of these buildings could potentially be very long. Several studies have
conducted a great deal of research into human behaviour and evacuation in high rise
apartment (residential) buildings. The major findings are summarized as follows:
• Proulx [44] & [45]: The pre-movement time in an actual apartment (residential)
building fire are found to be in a range of 0.5 minutes with good alarm and
192 minutes with no alarm (more than 3 hours), depending on the following factors:
37
o Alarm type and audibility.
o Visual access
o Responsibility for others
o Training
o Weather
In Proulx’s studies, some occupants did not evacuate i.e. chose not to evacuate and
waited for fire brigade.
• Brennan [46]: The pre-movement time in a night time apartment (residential) building
fire is in a range of 0.5 – 20 minutes. However, almost half of the building occupants
did not evacuate for first few hours; i.e. did not know (are not alert or awake), did not
respond to door knocking, or chose not to evacuate.
• VUT [47]: 50% of occupants in a residential building did not evacuate for first few
hours in a case of a real fire.
• SFPE [48] stated that “Alertness and limitation: A fire in the middle of the night in a
hotel or residential building will require a longer time to respond since most
occupants will be asleep. Another dimension to this characteristic is the possibility
that occupants may have some limitation that will extend their response time. These
limitations could be perceptual, physical, or intellectual, or might be due to the
consumption of medication, drugs, or alcohol. It is important to estimate the
proportion of occupants who will have a longer delay time to start due to alertness
conditions or a limitation.” In addition, the SFPE also stated that if the building often
has false alarms, it could be expected that the delay time to start will be extensively
extended since building occupants are unlikely to look for information and will be less
receptive to other cues.
From the literature, it is understood that, in the worst case scenario, occupant evacuation in a
high-rise building could potentially take up to several hours to the outside of the building due
to poor alarm notification, lack of training, frequency of false alarms, alertness and limitation,
unfamiliarity with the building fit-out.
38
4.4 Study on the Health Effect of Exposure to A Transformer Fire
4.4.1 Fitzgerald et al. (1981)
The American medical association, and the American Academy of occupational medicine and
society for occupational and environmental health studied the health effects to patients, who
were potentially exposed to polychlorinated biphenyls (PCB’s), and polychlorinated dibenzo-
p-dioxins (PCDF’s) from an electrical transformer fire in New York on February, 1981 [49].
The transformer fire occurred in the basement mechanical room of an 18-story structure in the
city centre. Approximately 681 litres of Askarel oil (65% PCB’s – Aroclor 1254 and 35%
polychlorinated benzenes) leaked from a transformer. The toxic gases produced by the
transformer were spread throughout the building via the two ventilation shafts.
A health survey was conducted three years after the fire and a total of 479 occupants of the
building and firefighters were studied in the research. The survey has achieved an excellent
response rate from the participants; almost 80% returned their questionnaire. As the results
were analysed, it was found that skin itching (23.7%) was the most commonly reported
symptoms after the fire and other symptoms included headaches (22.5%), nervousness or
sleep problems (20.3%), rashes or dermatitis (20.1%) and vision changes (17.4%). In addition,
several occupants were diagnosed to have an invasive cancer after the fire, which included a
thyroid cancer diagnosed in 1982, a lung cancer and a brain tumour diagnosed in 1984.
4.4.2 Eschenroeder & Faeder (1988)
The objective of Eschenroeder and Faeder’s study [50] is to estimate the risk of health effects
due to the inhalation of combustion products from mineral oil transformer fires using Monte
Carlo analysis. This is a means of statistical evaluation of mathematical functions using
random samples. In the research, Eschenroeder and Faeder have considered polychlorinated
dibenzofurans (PCDF’s) from the pyrolysis of polychlorinated biphenyls (PCB’s) as the main
toxic products that would be produced in an event of accidental fires involving mineral and
Askarel mixture oil insulated transformers. The two main findings of the report were the
cancer risk and the birth defect (health hazard) associated with a mineral and Askarel mixture
oil transformer fire.
39
As defined in the report “the definition of risk is based on a chance event derived from model
uncertainties rather than physical events”. Therefore, estimation is highly dependant on the
existing statistical data. Hence, this report has included the uncertainty study which can
provide quantitative measures of health conservatism by assigning confidence levels to
different numerical estimates. As a result of the analysis, the health risk from PCB-
contaminated mineral oil transformer fire was found to be insignificant both in case of cancer
burden and in the case of birth defects. Based on the Monte Carlo results, the probability of
the occurrence of a cancer burden of unity and to the health hazard burden of unity was found
to be 1.6 x 10-9 and 1.7 x 10-14, respectively.
40
4.5 Experiment on Transformer Oil Fire
4.5.1 Heskestad & Dobson (1997)
Heskestad and Dobson [51] reported two experiments on pool fires of transformer oil burning
over a rock bed in a 1.2 m diameter pan and the report was published in the Fire Safety
Journal 1997. The difference between the two tests was that one had drainage at regression
rates of 16 to 26 mm/min from the bottom of the plan and one was without drainage. The
simple transformer oil used for the experiments has a flash point of 157ºC (See Section 4.8 for
the comparison of the transformer dielectric fluids properties). As the results of the
experiments, the peak convective heat release rate from the transformer oil burning was found
to be between 750kW and 1MW. The HRR curve from both tests is shown in Figure 4-1 and
Figure 4-2.
Figure 4-1: Convective HRR of transformer oil with no drainage, extracted from Heskestad & Dobson
(1997)
Figure 4-2: Convective HRR of transformer oil with drainage, extracted from Heskestad & Dobson
(1997)
41
4.6 Transformer Ageing
4.6.1 Bartley (2000, 2002 & 2003)
William H. Bartley has been investigating transformer failure, transformer ageing and
transformer life cycle management with Hartford Steam Boiler Inspection & Insurance Co.
U.S. since year 2000. Five of the relevant articles are:
• Analysis of Transformer Failures – A Twenty Year Trend, (Bartley 2000 [52])
• Life Cycle Management of Utility Transformer Assets (Bartley 2002 [53])
• Analysis of Transformer Failures (Bartley 2003 [29])
• Investigating Transformer Failures (Bartley 2003 [54])
• Transformer Asset Management (Bartley & James 2003 [55])
Bartley has highlighted that transformer ageing is one of the main issues causing transformer
failures. Unlike other common causes of failure, such as failure due to electrical disturbances,
insulation issues, maintenance issues, lighting, loose or high resistance connection,
overloading and sabotage, transformer failure due to transformer age is very difficult to
identify. Based on Bartley’s studies, the mean age at failure for utility transformers was found
to be 17.7 years as shown in Figure 4-3.
0-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30 31-33 34-36 37-40 41-43 44-46 47-50 50+
Age of failure
Num
ber o
f fai
lure
(Note that the number of failures was missing in the original report)
Figure 4-3: Number of transformer failures, reproduced from Bartley 2000 [52]
42
Further to Bartley’s discussion [52], an equation was developed to predict the future
transformer failure as follow:
Equation 4-1: t
t
t eef β
β
μαω
++
=1)(
where f(t) is the instantaneous failure rate
ω is a constant for random events (0.005)
α is a constant
µ is a constant
β is a time constant
t is time (year)
Based on the data recorded by Hartford Steam Boiler Company, the property damage due to
transformer failure and fire, excluding business interruption losses, was found to be
approximately USD$9 per kVA in an average five years period. This extrapolates to
USD$6,750 for a 750kVA transformer.
43
4.7 Cost Effective Comparison between Different Types of Transformers
4.7.1 Goudie & Chatterton (2002)
Goudie and Chatterton [56] reported a comparison between the use of dry (solid or gas) type
and liquid type transformers in distribution substations at the standpoint of economics and the
environment with regards to the transformer lifetime. This report also compared the common
transformer dielectric fluids in terms of the economic, environmental and life safety factors.
Overall, the report concluded that the use of liquid type transformers would have more benefit
than dry type transformers and the main discussions are summarised as follow:
• Liquid type transformers are more efficient then a dry type transformer; in other words,
the energy loss by using a dry type transformer is much higher than a liquid type
transformer
• Less carbon dioxide would be produced by using liquid type transformers
• Dry type transformers may require higher maintenance cost due to periodic cleaning
since the coils are open to dust and pests.
• Typically, dry type transformers are physically larger than liquid types and, hence,
larger cores may be required that would lead to have a higher iron or core loss.
Furthermore, the report also provided an initial cost relationship of transformer. It used the
cost of a mineral oil filled transformer as a base point and measure the relative initial cost for
other type of transformers. The table is extracted from the original article and shown in the
following figure:
Figure 4-4: Initial cost for transformer dielectric materials, reproduced from Goudie & Chatterton
(2000)
44
4.8 Studies on the Dielectric Fluids
The properties of transformer dielectric fluid have been summarised in the table below from
the relevant literature. These literature include Oommen [19], Mcshane [21], Goudie and
Chatterton [56], Babrauskas [57], Bertrand [58], ASTM D4652-92 [59], ASTM D3487-00
[60], ASTM D2283-86 [61], Trabulus [62] and Patel [63].
Table 4-1: Properties of transformer dielectric fluid: Typical Values/ Limits
Properties Units Mineral Oil Silicone Oil
Vegetable Oil Askarels
Dielectric Breakdown kV 30 - 85 35 - 60 82 - 97 35 Relative Permittivity at 25°C 2.1 - 2.5 2.6 - 2.9 3.1 - 3.3 3.7 - 4.9
0 °C mm2.s-1 <76 81 - 92 43 - 77 Not stated 40 °C mm2.s-1 3 - 16 35 - 40 16 - 37 31 - 92 Viscosity 100 °C mm2.s-1 2 - 3 15 - 17 4 - 8 Not stated
Pour Point °C -30 - -60 -50 - -60 -19 - -33 -14 - -44 Flash Point (open cup test)
°C 100 - 170 300 - 310 310 - 328 None to boiling
Fire Point (open cup test)
°C 110 - 185 340 - 350 350 - 360 None to boiling
Density at 20°C (specific gravity)
kg.m-3 830 - 890 960 - 1100 870 - 920 1380 - 1570
Specific Heat capacity kJ.kg-1K-1 1.6 - 2.39 1.5 - 2.04 1.5 - 2.1 Not stated
Thermal Conductivity W.m-1 K-1 0.11 - 0.16 0.15 0.16 - 0.17 Not stated Expansion Coefficient 10-4.K-1 7 - 9 10 - 10.4 5.5 - 5.9 7
Heat of combustion MJ.kg-1 45.9 28 35 Not stated Moisture content, dry oil ppm 10 - 25 50 50 - 100 30
Volume resistivity at 25°C Ω.cm 1014 - 1015 10 14 10 14 10 11
Interfacial tension at 25°C dynes/cm 40 – 45 25 25 Not stated
Heat release rate 1 kW/m2 >1000 (1538 - 1625) < 1000 Note stated Not stated
1 Typical HRR for mineral oil is found as indicated in the bracket
45
CHAPTER 5 DATA COLLECTION
5.1 Statistical Studies
5.1.1 Sources of Data
The statistical data given in this section is based on three databases: (1) the annual statistics
from the Ministry of Commerce in New Zealand, (2) the fire incidents statistical data from the
Fire Incident Reporting System (FIRS) managed by the New Zealand Fire Service (NZFS)
and (3) the fire incidents statistical data from the National Fire Incident Reporting System
(NFIRS) managed by the National Fire Protection Association (NFPA).
The Ministry of Commerce, now known as the Ministry of Economic Development (MED), is
a government department responsible for the government ownership of public properties. The
number of distribution substations and the population in New Zealand are provided in their
annual statistics reports (Refer to Section 5.1.3). It was found that the population in New
Zealand is increasing with an average growth rate of 1.5% per year over the past 50 years.
This information implies that increasing number of high-rise buildings is required due to the
growing population in New Zealand. As a result, distribution substations are expected to
become more commonly built in buildings due to the higher loading density. The statistical
data on the number of distribution substations in New Zealand was obtained from the MED
between 1946 and 1995. Since the statistical data after 1995 was not available, the number of
distribution substations between 1995 and 2006 is estimated based on the growth rate
measured in the previous 50 years.
The purpose of the FIRS system is to collect and analyse data on fire incidents from the Fire
Services throughout New Zealand. Generally, the fire incidents can be classified mainly in
terms of their property types, location of fire origin, item first ignited and heat source.
According to the NZFS FIRS instruction and coding manual [64], the specific property use of
46
“6401- substations, transformers and power lines” is found under Code 64: Utilities and
Energy distribution. As the location of fire origin, the switchgear areas and transformer vaults
are found in Code 173. Based on these two criteria, 24 fire incidents were selected from the
NZFS FIRS database during the 6 years period from January 2000 to January 2006 [65]. Out
of the 24 fire incidents, 20 fire incidents are related to distribution substations and 4 fire
incidents are related to power or terminal substation. It is noted that the statistical data from
the NZFS FIRS provided only the significant information to the fire incidents, such as the
incident time frame, the incident type, the fire cause and the consequence. No specific
information was recorded in these incident reports, such as the characteristic of the properties,
the number of fatalities and the cost of property damages. Therefore, the consequence of
structure fires originating in switchgear areas or transformer vaults reported to the NFIRS [66]
is also examined in this research for reference.
5.1.2 Historical Case Study for Transformer Fires
Two critical distribution substation fire incidents reported between 2000 and 2006 in New
Zealand are discussed in this section. These fire incidents were all involved with transformer
fluid. Since no further investigation reports were found, the discussions are based on the
incident reports provided by the NZFS. These reports briefly record information about the fire
and the message log during the incident; however, the consequence of these fires was not
clearly stated. Due to the low number of transformer fire incidents occurred in New Zealand,
three additional transformer fire incidents in U.S. are discussed in this section for reference.
On the 24th January 2002, a distribution transformer in Napier caught fire. The heat source
was estimated to be electrical arcing and the first ignited material was transformer fluid. Of
the 20 fire incidents involving distribution substations, this incident was the only one that
mentioned the performance of the detection system. According to the incident report, a smoke
detector was installed in the building and was monitored. However, although the detector was
installed so it operated in an event of fire, it was not a factor in discovery of this fire. In this
case, the Fire Service was alerted by an emergency call 111 from an occupant. No information
about casualties and property damages was found in the incident report.
47
On the 21st June, 2003, an 11kV/415V step-down transformer was totally involved during a
fire in Christchurch. It is different to the previous incident as the ignition source in this case
was arcing from a faulty, loose or broken conductor and the first ignited object was the
electrical wire and wiring insulation, followed by the transformer fluid. When the Fire Service
arrived at the scene, the fire was already fully developed in the distribution substation.
Therefore, the firefighters decided to take no action until the power for the whole street was
turned off as it was extremely dangerous. Later, the fire was confined to the structure of origin.
As a result of the fire, the structure was badly damaged but no injuries were recorded.
In the morning of 24th July, 1984, a transformer fire occurred at the New York University
Medical Centre and was followed by an explosion. As Ragusa [67] stated, there were a total
of four transformers on the site. These transformers were 13.8kV/ 460V step-down
transformers. Mineral oil was used as the cooling medium and the units were installed in a
distribution substation. The cause of the fire was believed to be that the unit was overheated
and ignited the leaked transformer oil. There were no injuries in the event. Damage to the
equipment was not given in this article.
Another distribution transformer fire was discussed by Courtney [68]. The transformer fire
occurred in 1988 when the power was restored after a shut down for repairs. The fire ignition
source is believed to have been electric arcing inside the oil insulated transformer. As a result
of this transformer fire there were a total of four casualties; one minor and three serious
injuries, and property damage of USD$23,000 (1988).
A distribution transformer caught fire in a hospital in 1996 as Tremblay [69] stated. The
hospital is a three storey building with FRR construction, however the nature of the fire rated
construction was not recorded. Smoke detection systems and sprinkler systems were installed
throughout the building. The transformer fire was detected by the detection systems soon after
the fire started and was successfully extinguished by the sprinkler systems, which was
activated by the Fire Service. The cause of the fire was that the unit was overheated and
ignited the leaked transformer oil. Due to the early occupant warning alarm, there were no
injuries as a result of this transformer fire. The fire was confined to the room of origin and
property damage was estimated to be USD$10,000 (1996).
48
5.1.3 Number of Distribution Substations in New Zealand
According to the data from the MED database: the New Zealand Energy and Resources
Division and Market Information and Analysis Group [70], the New Zealand Energy
Modelling and Statistics Unit [71] and [72], and the New Zealand Ministry of Energy [73],
the number of distribution substations in New Zealand increased from a total of 24,000 in
year 1946 to 140,000 in 1995 as shown in Figure 5-1. These distribution substations might
contain a single or multiple transformer(s) with a voltage rating of 11kV or less. Based on the
available data, the growth rate is estimated to be 1.71% per annum as the solid line shown in
Figure 5-1. Following the estimated growth rate, the number of distribution substations in
2006 is determined to be 167,000. The data is listed in Appendix C.
Number of distribution substations in NZ from 1946 to 2006
0102030405060708090
100110120130140150160170180
1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006Year
Num
ber o
f dis
trib
utio
n su
bsta
tions
(100
0)
Statistics Data Estimated result Linear (Statistics Data )
Figure 5-1: Number of distribution substations in New Zealand from 1946 to 2006
49
5.1.4 Fire Incidents Reported to the NZFS FIRS
Each year between 2000 and 2006, an estimated 4 fire incidents were reported to the NZFS
FIRS in relation to the specific property use of substation and the fires originating in
switchgear areas or transformer vaults as shown in Figure 5-2. Of the 24 fire incidents during
the 6 year period, 20 involved indoor transformers. With these fires, only one injury was
reported to the NZFS FIRS. In addition, the property losses associated with the fire incidents
could not be found from these incident reports. The statistical data addressed in this section
include:
Number of distribution substation fires
Monthly trends
Time of day
Equipment involved
Source of ignition
Primary ignition object
Indicated cause
Avenue of flame/ smoke travel and their extent damage
Note that the statistical data of the above phases are attached in Appendix C.
Number of distribution substation fires:
There are a total of 20 fires originating in distribution substations reported to the NZFS FIRS
during the 6 year period between 2000 and 2006 with a peak of five incidents in the year
2002/03. The best year is found to be the year 2001/02. No fires originating in distribution
substations were reported in this period. An average of three to four fire incidents in
distribution substations is determined based on the data.
50
Number of fire incidents reported to the FIRS in 2000/06
0
1
2
3
4
5
6
2000/01 2001/02 2002/03 2003/04 2004/05 2005/06
Year (ended Jan)
Num
ber o
f fire
s
Figure 5-2: Number of distribution substation fires in 2000/06 (Source NZFS FIRS)
Monthly trends
As illustrated in Figure 5-3, the majority of such fires occurred between June and August with
a peak in the winter month of June. It was followed by the summer season (December -
February). The frequency of the fires is less in spring and autumn (March - May and
September - November). This result can be explained by the power consumption. In general
buildings, heating and air-conditioning equipment, such as heaters, are often the largest power
consumers. As the power consumption increases, the probability of overloading will also
increase. According to Hattangadi [28], even though overloading may not directly cause the
failure, it may reduce the equipments useful lifetime (Refer to Section 5.2). Specifically, it
may be dangerous when overloading equipment that has been in service for more than 30
years. The accuracy of the analysis could be improved when more data is available.
51
Monthly trends for distribution substation fires in 2000/06
0
1
2
3
4
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Num
ber o
f fire
s
Figure 5-3: Monthly incidence of distribution substation fires in 2000/06 (Source NZFS FIRS)
Time of day
Figure 5-4 shows the hourly trends for distribution substation fires in the period between 2000
and 2006. Typically, these fires are equally distributed into six periods of time. As can be
seen, these fires are most likely to occur during ‘work’ hours; between 7am and 3pm, as 9 out
of 20 fire incidents occur during these times. It may be again due to higher power
consumption during the day than at night.
Hourly trends for distribution substation fires in 2000/06
0
1
2
3
4
5
6
23:00 ~ 03:00 03:00 ~ 07:00 07:00 ~ 11:00 11:00 ~ 15:00 15:00 ~ 19:00 19:00 ~ 23:00
Time of day
Num
ber o
f fire
s
Figure 5-4: Hourly trends for distribution substation fires in 2000/06 (Source NZFS FIRS)
52
Supposed Causes
According to the NZFS FIRS data, the supposed cause of distribution substation fires can be
classified into five groups: (1) Electrical failure, (2) Mechanical failure, (3) Equipment
overload, (4) Lack of maintenance and (5) Unknown causes. Figure 5-5 illustrates the leading
causes of these fires. The dominant causes are electrical failure (60%); of which 20% were
due to short circuits or earth faults and 40% from other electrical failure. The second leading
cause of these fires is equipment being overloaded (20%).
Supposed cause
Equipment overloaded (includes electric cords serving too many appliances)
20%
Mechanical failure, malfunction
10%
Unknown5%
Electrical failure60%
Lack of maintenance5%
Figure 5-5: Causes of distribution substation fires (Source NZFS FIRS)
Primary ignition object
Generally, the combustible materials in distribution substations may include the electrical
wire or cable insulation, transformer (e.g. transformer fluids) and other known items (e.g.
wood board and chairs). As a result of the data analysis, 65% of these fires had the electrical
wire or cable insulation as the object first ignited (Figure 5-6). Compared to the cable
insulation, the probability of having transformer or transformer fluid as the object fist ignited
is much lower (20%); however, the consequence of transformer fluid fire could be worse.
53
Object first ignited
Other known objectfirst ignited
15%
Electrical wire, Wiring insulation
65%
Transformer, Transformer fluids
20%
Figure 5-6: Object first ignited (Source NZFS FIRS)
Equipment involved
According to the NZFS FIRS instruction and coding manual [64], the term of equipment
involved represents “the equipment that provided the heat for the fire to start, or was involved
in the release of hazardous substances”. It may sometimes be very difficult to define the
equipment involved in some incidents. Out of the 20 fires, there were 6 fires where the
equipment involved was not recorded (30%). For the known equipment, there were 7 fires
(35%) involving transformer and associated equipment with distribution type recorded. It is
followed by the circuit breakers associated with transformers (20%) as the leading type of
equipment involved. Other known equipment include the power cables, controlling switches
and other not classified items (15%).
54
Equipment involved
Circuit breakers associated with
transformers20%
Transformer & associated equipment -
Distribution type35%
Other known equipments
15%
Information not recorded
30%
Figure 5-7: Equipment involved (Source NZFS FIRS)
Source of ignition (Heat source)
As the source of heat causing ignition, 70% of these fires involve arcing, either from the short
circuit (60%) or from another faulty, loose or broken conductor (10%). Out of the 60% of
fires that involved short circuit arcing as the heat source, 5% were caused by water, 10% were
from the defective or worn insulation and 45% were unspecified. There are 10% of these fires
that have the source heat recorded as overloaded equipment.
Heat source
Other known heat source20%
Heat from overloaded equipment
10%
Arc from fault, loose or broken conductor
10%
Short circuit arc60%
Figure 5-8: Source of ignition (Source NZFS FIRS)
55
Extent flame/ smoke damage
Figure 5-9 illustrates the extent of flame and smoke damage for the 20 fire incidents analysed.
As can be seen in the figure, there are only 12 fires reported to the NZFS FIRS that report the
extent of damage. For the extent of flame damage, five incidents were confined to the object
of origin and six incidents were confined to the structure of origin. Out of these 6 fires
confined to the structure of origin, four incidents involved a transformer, with the transformer
fluid as the ignition object. This information supports the concept of having transformer fluid
involved in the ignition of a fire being a low occurrence and high consequence event. The
avenue of flame travel includes the flammable liquid (2 fires), furniture and fixtures (1fire) or
structural member allowing vertical (1 fire) or horizontal travel (1 fire), such as a wall burned
through, inadequate fire stopping, air handling ducts, service/pipe shaft or failure of rated
assembly. Smoke may not cause any damage if the fire is small enough and the smoke is well
controlled by the ventilation system. Similar to flame damage, the fires confined to the
structure of origin often had transformer fluid involved as the object ignited.
Extent of flame/smoke damage
0
1
2
3
4
5
6
7
8
9
No damage ofthis type
Confined toobject of
origin
Confined to topart of room
or area oforigin
Confined toroom of origin
Confined tostructure of
origin
Beyondstructure of
origin
Unknown
Num
ber o
f fire
s
Extent of smoke damageExtent of flame damage
Figure 5-9: Extent of flame/ smoke damage (Source NZFS FIRS)
56
5.1.5 Fire Incident Reported to the NFIRS (U.S.)
Number of structure fires originating in switchgear areas or transformer vaults
Figure 5-10 illustrates the number of structure fires originating in switchgear areas or
transformer vaults during the 22 years period between 1980 and 2002 [66]. As can be seen,
there are a total 1890 structure fires originating in distribution substation recorded by the
NFIRS in 1980. Since then, the number of fires is decreasing every year with an average
decline rate of 55 fires per year as shown by the solid line in Figure 5-10. Until recently in
2002, the number of fires reduced to 680 fires.
Boykin [74] states that the total number of transformers in the U.S. is found to be 23.1 million
in 1982. Using the same growth rate of 1.71% per annum as determined in Section 5.1.3, the
number of transformers in the U.S. is estimated to increase to about 30 million in 2006.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Year
Num
ber o
f Fire
Fire Incident
Linear (Fire Incident)
Figure 5-10: Number of structure fires originating in switchgear areas or transformer vaults between
1980 and 2002 (Source NFIRS)
57
Life safety consequence
The life safety consequence is categorised into two types in the NFIRS data: civilian injuries
and civilian deaths. Figure 5-11 and Figure 5-12 illustrate the number of civilian injuries and
civilian deaths, respectively, of the structure fires originating in switchgear areas or
transformer vaults between 1980 and 2002 in U.S. The data is also attached in Appendix C.
While the number of fires is decreasing every year as shown in Figure 5-10, the number of
civilian injuries also decreased from an average of 88 injuries before 1995 to an average of 33
injuries after 1996 as shown in Table 5-1. Moreover, although the average number of injuries
per fire decreased from 0.06 to 0.04, the number of deaths per fire increased from 0.002 to
0.003 after 1996.
Table 5-1: Life safety consequence of distribution substation fires between 1980 and 2002 reported to the NFIRS
Year Number of fires
Civilian deaths
Deaths per fire
Civilian Injuries
Injuries per fire
Before 1995 (per year) 1421 3 0.00194 88 0.06177
After 1996 (per year) 863 2 0.00281 33 0.03874
Overall (per year) 1251 3 0.00212 71 0.05693
In regards to life safety, 1999 and 2002 were found to be the worst and the best year
respectively, out of the 22 year period. There were a total of 41 civilian injuries and 6 civilian
deaths in 880 fires in 1999 and a total of 18 injuries and no deaths in 680 fires in 2002.
58
Civilian injuries
0
20
40
60
80
100
120
140
160
180
200
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Year
Num
ber o
f inj
urie
s
Figure 5-11: Civilian injuries as a result of structure fires originating in switchgear areas or
transformer vaults between 1980 and 2002 (Source NFIRS)
Civilian deaths
0
2
4
6
8
10
12
14
16
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Year
Num
ber o
f dea
ths
Figure 5-12: Civilian deaths as a result of structure fires originating in switchgear areas or transformer
vaults between 1980 and 2002 (Source NFIRS)
59
Property damage
For the structure fires originating in switchgear areas or transformer vaults reported to the
NFIRS between 1980 and 2002, the average property loss is determined to be NZD$50.5
million per year and NZD$40,400 per fire. Note that the costs given in the original data [66]
is in USD$ and are converted to NZD$ using the average currency exchange rate of 1.54 [75].
Figure 5-13 illustrates the direct property damage of these structure fires originating in
switchgear areas or transformer vaults between 1980 and 2002 in the U.S. in terms of the total
property damage costs per year (bar chat), as well as the cost per fire in each year (line curve).
The data of these structure fires is referred in Appendix C.
Figure 5-13: Directly property damage as a result of structure fires originating in switchgear areas or
transformer vaults between 1980 and 2002 (Source NFIRS)
As can be seen, the largest total direct property damage costs of NZD$76.2 million is found in
1993, while the lowest total costs of NZD$20 million is in 1999. However, when determining
the average cost per fire, 2001 is shown to be the worst year and the cost per fire is
NZD$95,800. This is due to the relatively low number of fires in 2001 but high property loss
from each fire.
60
5.2 Reliability Data
5.2.1 Transformer and Associated Equipment
Transformers impact distribution system reliability in two related ways: overloads and
failures. Transformers may get overloaded from time to time and failures may occur when the
transformer is operating with an overload. Overloads may cause the oil temperature to rise up
to over the permissible limits, typically 90°C. Hattangadi [28] states that for every 6°C rise in
the oil temperature above the permissible limits, the useful life of the transformer is reduced
by a period of time which is double the period for which the transformer is operating under
the normal temperature. In other words, when a transformer operates with oil temperature of
102°C for one hour, the useful life of the transformer is reduced for approximately four hours.
Other potential causes of transformer failure can be found in Section 2.3.4.
From a literature, the typical failure rate of distribution transformers is found to be about 0.02
to 16 failures per 106 operation hours as shown in Figure 5-14. This range of transformer
failure rate also agrees with the failure rate found from other studies such as Green [76] and
the American Institute of Chemical Engineers [77]. Hence, the number of failures per year is
determined to be in the range of 180 x 10-6 to 140 x 10-3 failures per year.
Figure 5-14: Typical failure rates for various equipment (Extracted from Fig. 11.1 of Moss [30])
0.02 16
61
The failure rates for the distribution transformer and associated equipment, such as the circuit
breaker, power cable, capacitor, fuses and the relevant fire protection systems, are obtained
from Moss’s reliability data handbook [30] as shown in Table 5-2. Failure rate, which is
known as a function of time, can generally be defined as the number of failures for a device
within a unit of time. As can be seen, the failure rate of the transformer and associated
equipment is generally low. The entire transformer systems are always protected and
monitored by many protection systems. It is considered that transformer failures may not
necessary result in a fire; hence, the probability of transformer fire can be expected to be
lower. In addition, the reliability of fire protection systems is relatively low when compared to
the transformer and associated equipment. Note that these failure rates are provided solely for
information purpose and are not used in the analysis in the report.
Table 5-2: Failure rate for transformer and associated equipment and some fire protection systems Failure per 10^6 hour Failure / year Transformer and associated
equipment Lower Mean upper Mean Distribution transformer 0.02 2.53 16 22 x 10-3
Circuit breaker 0.5 1.03 10 9 x 10-3 Power cable 0.5 2 2.5 17 x 10-3 Capacitor 0.0004 0.007 0.075 61 x 10-6 Fuses 0.0265 0.634 2.36 6 x 10-3
Fire protection systems Fire damper 5 13.7 29.6 120 x 10-3 Fire fighting system 0.05 36 123 314 x 10-3 Fire alarm Not stated 31.9 Not stated 279 x 10-3 Smoke detection system 6 Not stated 6.7 56 x 10-3 Sprinkler system Not stated 0.5 Not stated 4.4 x 10-3
5.2.2 Fire Protection Systems
Often, the reliability of fire protection systems can be classified into two types, operational
and performance reliability. Operational reliability is an estimate of the probability that the
system can successfully operate in a fire event. This reliability can be improved with a good
maintenance programme. Performance reliability is an estimate of the system adequacy once
it has operated. However, as the following reliability data is sourced from various studies, in
which the scope, boundaries and breadth may vary significantly, it may not be precise but it
62
could provide an accurate representation of the trend. Note that Table 5-3 and Table 5-4 may
consist of studies published in the late 1970’s. As expected, standards and codes are
improving year-on-year in order to provide equivalent or even higher level of fire safety to the
public. In other words, modern fire safety systems are likely to be more reliable and more
effective than these fire safety systems maintained using the old standards and codes.
Therefore, the analysis including these old data can result a conservative design.
In addition to the reliability of the fire safety systems, the year shown in the tables indicates
when these papers were published. Most of these published papers contained the statistical
data from a couple years up to a period of 100 years. For system reliability, the more data
being studied the better and more comprehensive results that can be obtained. Therefore, these
data are considered to be relevant and appropriate for the analysis.
Smoke detection system
As per the prescribed requirements described in Section 1.1, more than half of the standards
and guidelines studied have recommended smoke detection systems be installed in the
distribution substations in lieu of heat detection systems. Thus, the reliability of smoke
detection systems is used for the assessment and, hence, is discussed in this section.
The reliability of smoke detector systems is expressed as the probability that the smoke
detector will be activated in the event of a fire. Many researchers have studied the
performance of smoke detection system in specific types of buildings or in any buildings in
general. However, no information is found about the reliability of smoke detection systems in
distribution substations specifically. Hence, the reliability of smoke detection systems for
general buildings is used for the assessment in Section 7.6.2. Some of the articles that do not
provided the reliability of smoke detection systems for general buildings, an average value
will be used from the reliabilities of smoke detectors for commercial, residential and
institutional occupancies. Table 5-3 shows the reliability of smoke detection systems for
general buildings based on the following literature: Bukowski, Budnick, Schemel [78], and
Yung et al. [79].
63
Table 5-3: Reliability of smoke detection systems
Type of detector Reliability of smoke detection system Original reference
Smoke detector 85.7% Warrington Delphi UK (1996)
Smoke detector 82.5% Fire Engineering Guidelines Australia (1996)
Smoke detector 94.0% Tokyo Fire Department (1997)
Smoke detector 89.0% Watanabe (1979)
Smoke detector 77.8% Bukowski, Budnick, Schemel (1999)
Smoke detector 80.0% NRCC (2006)
Automatic suppression systems
As Thomas [80] stated, the performance of automatic sprinkler suppression systems can be
defined into four categories, as follows:
1. The fire is too small to activate the sprinkler system
2. The sprinkler system should have been activated but did not
3. The sprinkler system is activated and controlled the fire but did not extinguish the fire
4. The sprinkler extinguished the fire
The first category refers to a scenario where a small fire may self-extinguish due to lack of
fuel or oxygen. In this case, the smoke layer temperature is expected to be low and not
sufficient to activate the sprinkler heads. However, in the case of a transformer fire initiating
in a distribution substation, a sufficient fuel load is expected to be in the room, such as
dielectric material, electrical equipment, power cables and the transient combustible materials.
Unless the distribution substation consists of oxygen control system, which may immediately
reduce the oxygen level when fire is detected, transformer fires are expected to burn
continuously and to be large enough to activate the sprinkler heads. Since the use of oxygen
control system is not a subject of this study, the first class is not considered to be possible in
the case of transformer fires.
The three other categories are separated into two phases: success and failure. The sprinkler
system is considered to have failed if it is not activated in a fire (Category 2), whereas the
system is considered to be a success once it is activated regardless of it controlling or
64
extinguishing the fire (Category 3 and Category 4). Many previous reports have proved that
the leading reason for the unsatisfactory sprinkler performance is due to human error, such as
failure to maintain the operational status of the system, and failure to assure the adequacy of
the system for complete coverage of the current hazard. Similar to smoke detection systems,
the reliability of sprinkler systems for general buildings is used for the assessment in this
research due to the unavailability of data about the performance of sprinkler systems in a
distribution substation. Table 5-4 shows the reliability of sprinkler systems for general
buildings based on the following literature: Bukowski [78], Yung [79], Taylor [81],
Spearpoint [82], Koffel [83], Budnick [84], Rohr [85], Richardson [86], Risk Logic Inc. [87],
Miller [88] and Marryatt [89].
Table 5-4: Reliability of Sprinkler systems Building
occupancy Reliability of sprinkler
system Original reference
General 95.0% Warrington Delphi UK (1996)
General 99.0% Fire Engineering Guidelines Australia (1996)
General 97.0% Tokyo Fire Department (1997)
General 92.1% BRE (1973)
General 96.2% Powers (1979)
General 96.7%- 97.9% Finucane et al. (1987)
General 96.0% Bukowski, Budnick, Schemel (1999)
General 90.0% NRCC (2006)
General 81.3% Taylor (1990)
General 97.2% Yashiro et al. (2000)
General 96.2% NFPA (1970)
General 95.7% US Navy (1977)
General 95.0% Smith (1983)
General 87.0% Ramachandran (1998)
General 86.1% Factory Mutual (1977)
General 85.8% Oregon State Fire Marshal (1978)
General 96.0% Budnick (2001)
General 93.0% Hall (2005)
General 96.0% Richardson (1985)
General 82.0% Risk Logic Inc (2006)
General 94.8% - 95.8% Miller (1974)
General 99.5% Marryatt (1988)
65
CHAPTER 6 FAULT TREE ANALYSIS
6.1 Introduction
Fault Tree Analysis (FTA) is understood to be “a system engineering method for representing
the logical combinations of various system states and possible causes which can contribute to
a specified event (called the top event)” as defined in the standard for risk management
AS/NZS 4360:1999 [90]. The tree structure, which is organised by logical dependency,
generally begins with the definition of a top event and then determines the probability of that
event through logical relationships, such as AND gates and OR gates. In general, AND gates
represent a situation where the top event is true only if all the lower events are true and is
false if one of the lower events are false. Inversely, OR gates represent a situation where the
top event is true if any one of the lower events is true and is false only if all of the lower
events are false. Typically, the probability of the lower events can be determined in three
ways; by examining the historical data, by expert engineering judgement or by evaluating the
scenario by using a model. As an output of FTA, the probability of the top event can be
estimated.
In this chapter, a typical fault tree is developed for a transformer fire in a distribution
substation as the top event. It is a sequence of events that could lead to the transformer fire,
which include the appearance of ignition sources, the appearance of combustible materials
and the availability of oxygen to the fire. By providing the expected fault rate of these lower
events, the probability of a transformer fire in a distribution substation can be estimated.
However, due to the lack of information about the fault rate of these lower events, the
probability of a transformer fire in a distribution substation is not determined but the structure
of the fault tree is given for reference.
66
6.2 Fault Tree
Based on the information discussed in Section 2.3.4, a typical fault tree for a transformer fire
in a distribution substation is developed as illustrated in Figure 6-1 through to Figure 6-3.
This fault tree is provided to show the necessary elements resulting in a transformer fire in a
distribution substation. Generally, three primary contributing factors must be present to result
in a transformer fire. These factors are:
1. Source of fuel
2. Source of oxygen
3. Source of ignition
Any materials that have the ability to combust are considered to be potential fuels for a fire or
explosion when an ignition source is provided. In distribution substations, the following
combustible materials are likely to be present. These include:
• Power cables and electrical equipment directly connected to the transformer;
• Dielectric material inside the transformer, including any substances inside them;
• Transient combustible materials, such as the wooden boards and chairs;
• Combustible vapour, which is generated by oil decomposition due to overheating.
Essentially, the occurrence of the above combustion material may be affected by several
factors, including the selection of materials for transformer system (e.g. non-combustible
dielectric materials (dry air), high fire resistance rated cables and other electrical components),
the reliability of protection systems and a good maintenance and management plan. All of the
above described factors should play vital role in determining the probability of occurrence of
the combustible material in the distribution substation. It should be noted that the presence of
combustible material is not always sufficient to cause a fire. In terms of this study, the
presence of fuel is considered to be effectively 100% otherwise no fire could occur.
67
As is known, fires may self-extinguish if there is not sufficient oxygen provided. The main
source of oxygen for a fire or explosion is the general body of air. From the literature review,
a new solution to limit transformer failure resulting in a fire has been developed and applied
in many modern distribution substations. As Allan [91] stated, “Successful designs have
involved the use of closed chambers where the transformers are immersed in an inert
atmosphere of nitrogen or CO2”. This solution could potentially reduce the level of oxygen
below that required to support combustion in the area. In this situation, the probability of
oxygen availability may rely on the oxygen control system. In other words, the presence of
oxygen may be reduced. Oxygen control system and its reliability are not studied in this
report..
As defined by Ainsworth et al. [92], “A source of ignition is anything that has the potential to
get hot enough to ignite a material, substance or atmosphere in the workplace”. For
distribution substations, the source of ignition can be classified into internal overheat and
external overheat. Internal overheating indicates that the heat is generated internally by an
equipment failure, such as electrical arc or sparking, and the protection devices are defective.
External overheating may include any exposure fires, such as arson, lightning strike or cable
overheat due to overload or cable degradation or the like.
68
Figure 6-1: Fault tree for the transformer fire
AND
3.1
Transformer fire in a distribution substation
AND
Combustible Material is present
1.0
Internal Overheat
3.1Cables and
Electrical Equipments
1.1
Ignition Source is present
3.0
Oxygen Availability
2.0
Dielectric Material
1.2
Transient Combustible Materials
1.3
Combustible Vapour
1.4
External Overheat
3.2
3.2
Transformer Oil Decomposition
1.4.1
Protection System Failure
1.4.2
AND gate
OR gate
OR OR
69
Figure 6-2: Fault tree for transformer internal overheat
Figure 6-3: Fault tree for transformer external overheat
Transformer Internal Overheat 3.1
AND
Figure 2-3
Transformer Failure
3.1.1
Electrical Protection Device Fault
3.1.2
Over Temperature Protection Fail
3.1.2.2
OR
Circuit Breaker and Fuses Fail
3.1.2.1 Overcurrent Relay Fail
3.1.2.3
Pressure Relief Device Fail
3.1.2.6
Excess Gas Protection Fail
3.1.2.4Sudden Pressure
Relay Fail
3.1.2.5
AND gate
OR gate
Transformer External Overheat 3.2
OR
Arson 3.2.1
OR
Cable Overheat
3.2.3
Lightning Strike
3.2.2
Overload 3.2.3.1
Cable Degradation
3.2.3.2
AND gate
OR gate
70
CHAPTER 7 EVENT TREE ANALYSIS
7.1 Introduction
The definition of risk is found in Standard AS/ NZS 4360:1999 [90]. It states that “Risk is the
chance of something happening that will have an impact upon objectives. It is measured in
terms of consequences and likelihood”. The standard further described that “Consequences
may be expressed in terms of monetary, technical or human criteria …and likelihood is
usually expressed as either a probability, a frequency or a combination of exposure and
probability…”.
Event Tree Analysis (ETA), which is a primary Quantitative Risk Assessment tool, is defined
in Standard AS/ NZS 4360:1999 [90]. It states that the ETA is “a technique which describes
the possible range and sequence of the outcomes which may arise from an initiating event”. It
is understood that ETA is a forward looking consequence technique. By identifying the event
of hazard as a root, the following outcomes, usually two potential outcomes (success or
failure), may develop in responding to the previous event and so on. Each branch probability
can be obtained by the product of the probability along the pathways and life safety
consequence is considered in the assessment. In order to allow a comparison between fire
safety designs, the consequences are translated into equivalent monetary values (EMV). Note
that the risk to building occupants is evaluated based on the number of fatalities, which is the
expected maximum number of fatalities resulting from a certain accident in the scenario.
As Barry [93] stated, risk can be estimated using the following equations:
Equation 7-1: ( )(C) esConsequenc
branch theofnumber j where
)(Pbranch each ofy probabilit theofProduct
(F) LikelihoodEvent
Fire Initiating
j ×⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
=
×⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=Risk
Equation 7-2: ∑ ⋅⋅=j j CPFRiskTotal
71
The steps for developing fire risk event tree are identified by Barry [93], as follow:
1) Identifying the initiating event and the pathway factors;
2) Structuring the event tree branches and evaluate the incident outcomes;
3) Quantifying the probability for the pathway factors in each branch;
4) Quantifying the consequences and translate them into the EMV;
5) Determining the fire risk estimation and record it for the cost-benefit analysis.
From the literature review, it is found that there are two major limitations of the ETA. The
first limitation of the ETA is that each event tree can only evaluate one identified initiating
event with the designed pathway factors. As stated in the Risk-based Decision-making
guidelines [94], “an event tree is not an exhaustive approach for identifying various causes
that can result in an accident. Other analysis techniques should be considered if the objective
of the analysis is to identify the cause of potential accidents.” Generally, the initiating event
and the sequence of outcomes in the event tree are to be primarily identified by other analysis
techniques, such as What-if, Checklist, Hazardous Operation Assessment (HAZOP) and
Failure Mode and Effects Analysis (FMEA). In the case of more than one initiating event or
any changes of the pathway factors in the event tree, independent event trees are required.
Based on this limitation, a total of 14 independent event trees are developed to assess the
scenarios with different fire safety design and transformer types in this report.
As the second limitation of the ETA, it is often difficult to define the probabilities
independently because the occurrence of the root events is usually dependent on the outcome
of prior events. The probability of success/ failure of the resulting events usually correlate to
the previous event. For example, if the detection system is failed, it could potentially delay the
arrival time of the Fire Service and result in influence of the success/ failure probability of
manual firefighting. However, many currently available data are likely to be measured
individually for the use of various systems and services. Therefore, these data may be
inappropriate as each event has its specific dependency in the event tree. To overcome this
limitation, significant literature review may be required to make sure the use of data is
appropriate.
72
Uncertainty is expected in the risk estimate due to the assumptions made and the uncertainties
of the data sources as discussed in Section 1.3. In the assessment, probability distributions
with boundaries will be used for these uncertain input parameters in the risk estimate
calculation. A software package, @Risk4.5, which is an additional function in Microsoft
Excel for extending the analytical capabilities of Excel, is used to conduct the Monte Carlo
simulations for the risk estimates.
In addition, where an array of values is found for the pathway factors, such as the reliability
of sprinkler systems and smoke detection systems, the Bestfit function in @Risk4.5 will be
used to fit the best distribution to data.
73
7.2 Model Overview
The primarily objective of this research is to evaluate whether four hour fire separation
between the distribution substation and the interior spaces of the building proposed by the
NZFS is a cost-effective solution to the occupants life safety in a typical New Zealand high-
rise building. Prior to the assessment, it is significant to define the characteristics of the model
building and the specifications of the distribution substation. Two approaches were carried
out to define a base building for the analysis. These include:
1. Site visits to the existing high-rise buildings in Christchurch, New Zealand in 2006.
2. Review of high-rise building plans.
Based on the above information, a model building with specified characterisations is defined
as a base building for the analysis in this research. A brief description of the model building
and the specifications of the distribution substation are listed in Table 7-1 and Table 7-2,
respectively.
Table 7-1: Model building characterisation
Location of the building - Central city
Building use - Commercial and residential mixed-use building,
Number of storeys and
building height
- The building contains 6 floors and has a total height of 21.6m with
3.6m height on each floor.
- The escape height is measured up to the floor of the top level and,
therefore, is 18m.
Purpose groups
- CM (retail shop) and ID (substation) at ground floor;
- SR (residential apartment) at 2nd floor up to the 6th floor (Refer to
Section 3.2)
Floor area - 800m2 per floor
Number of occupants
- Apartment floors: 6 apartments on each floor are estimated. As
Haag [95] stated, the occupant density is about 2.4 persons per
house. Total number of occupants in the apartments is therefore
estimated to be 72 people (2.4 persons/house x 6 houses x 5
74
floors)
- The floor area of the retail shop is assumed to be 400m2.
Therefore, the number of occupants in the building is determined
to be about 67 occupants based on 6m2 per person for retail shop
area as Bennetts et al. [96] stated.
- One or two contractors are expected to work in the plant room
regularly (e.g. maintenance, inspection and testing).
- Other space on the ground floor is assumed to serve the corridor,
lobby, lift, stairs or the like. No occupants counted as per the
C/AS1 precautions.
Means of escape - Two escape routes are provided in the building
Active systems
- According to the C/AS1 Clause 4.5.11, for SR purpose group
where any lower floor contains a purpose group other than SR
(e.g. CM retail shops, ID distribution substation), all lower floor
shall have either Type 3 (heat detector), Type 4 (smoke detector)
or Type 6 (Sprinkler). In this research, a Type 4 automatic fire
alarm system with smoke detectors and manual call points is to be
installed throughout the building and is monitored.
- Fire hose reels, Fire hydrant system and Fire panel board are
assumed to be in the building.
- Depending on the fire safety design in each scenario, sprinkler
systems may or may not be provided.
Table 7-2: Specifications of the distribution substation Location of the
distribution substation
The distribution substation is located on the ground floor having one
external wall with an access direct to the outside and an internal
access is provided to the building.
Room geometry W4m x L6m x H3.6m
Number of transformers One transformer (3-phase, 750kVA – 11kV/415V)
Combustible materials Dielectric material, cables and electrical equipment, transient
combustible materials and combustible vapour
Volume of oil
550 – 840 L for any liquid type transformer
Oil containment is installed.
(Applicable for liquid type transformer only)
75
Generally, distribution transformers can have power ratings of 300kVA, 500kVA, 750kVA,
1000kVA or more. Some recent researchers have found the average power consumption is
about 8 to 10kVA per New Zealand household. In this case, the model building is assumed to
include shops and apartments in a 6 storey building. Assuming there are 6 apartments on each
floor, the total power consumption is determined to be 360kVA. To be conservative, higher
total power consumption is expected. Therefore, a single 750kVA (3-phase, 11kV to 415V
step-down) transformer is considered to be adapted for the model building.
Through discussion with a senior sales engineer [97], it is understood that a 750kVA liquid
type transformer usually contains about 550L to 840L of transformer oil and the most likely
volume of oil is about 600L. Typically, the size of a 750kVA transformer is about L 1.5m x
W 1.5m x H 2m. Therefore, including the associated facilities, the floor area of the
distribution substation is estimated to be about 24m2 with a room ceiling height of 3.6m.
Two site visits were conducted to two distribution substations in New Zealand. One of which
is in the Christchurch city centre and another is at the University of Canterbury. Some
photographs were taken at these distribution substations as attached in Appendix A. From the
site inspections, some transient combustible materials are found in distribution substations.
These materials include wooden boards and furniture. Therefore, these combustible materials
should be included when considering the fire loads in the distribution substations.
The model building is assumed to be a non-sprinklered building sprinkler. It is understood
that in a sprinklered building, sprinkler system is likely to be extended to the distribution
substation inside and the costs of this extension is expected to be low. Therefore, the cost-
effectiveness of installing a sprinkler system in the distribution substation inside a sprinklered
building is expected to be higher than installing a sprinkler system in the distribution
substation inside a non-sprinklered building due to its low cost. To be conservative, this
research assesses the risk of transformer fire in a non-sprinklered building.
Recently, many new distribution substations often separate transformers, switchgears and
other low hazard electrical facilities by internal construction. This approach has two main
advantages: the first advantage is to reduce the probability of the electrical contractors to
work in a high risk indoor environment for a long time and another advantage is to prevent
small electrical or cable fires spread to the high hazard equipment. However, this research
76
primarily considers the fire risk exposure to the building occupants and the fire origin is the
transformer (not ignited from other exposure fires). Therefore, the internal construction
separating the equipment in a distribution substation is not considered to have a significant
benefit to the building occupants in this case. Therefore, this research will only assess a
transformer fire in a distribution substation with no internal constructions separating the
equipment.
77
7.3 Analysis Approach
A total of 14 scenarios with different fire safety designs and transformer types for a
distribution substation in a high-rise building are assessed in this research. In order to evaluate
the fire risk in a distribution substation with different fire safety designs separately, the same
type of transformer, Flammable liquid (mineral oil) insulated transformer, is used in the first
10 scenarios. Generally, the differences between these scenarios are the involvement of the
sprinkler systems and the use of different FRR construction. Simply, sprinkler systems are
considered to be either installed or not installed in the room. Five typical levels of FRR
construction are assessed, which are 30 minute FRR, 1 hour FRR, 2 hour FRR, 3 hour FRR
and 4 hour FRR.
Thereafter, two particular fire safety designs, i.e. 3 hour fire separation with no sprinkler
systems and 1 hour fire separation with sprinkler systems, are selected as a baseline for
analysing the transformer types. In Scenario 11 to Scenario 14, two types of transformers with
a low fire hazard, a less flammable liquid (silicone oil) insulated transformer and a dry type
(dry air) transformer, will be used to replace flammable liquid (mineral oil) insulated
transformer. The reason for selecting these two fire safety designs as the baseline in this part
is due to these two fire safety designs being recommended in the NFPA as mentioned in
Section 3.5. Note that NFPA is the only standard provided the fire safety protection
requirements for other types of transformers. A brief summary of the fire safety design and
type of transformer used in each scenario is shown in Table 7-3. Note that smoke detection
and alarm systems and manual Fire Service suppression are considered in all cases.
78
Table 7-3: A brief description of the fire protection systems combination for each scenario
Scenario Type of transformer Smoke
detection system
Sprinkler system
Manual fire suppression
system FRR
construction
1 Liquid Type (Mineral oil) Provided Not provided Provided 30 minute
2 Liquid Type (Mineral oil) Provided Not provided Provided 1 hour
3 Liquid Type (Mineral oil) Provided Not provided Provided 2 hour
4 Liquid Type (Mineral oil) Provided Not provided Provided 3 hour
5 Liquid Type (Mineral oil) Provided Not provided Provided 4 hour
6 Liquid Type (Mineral oil) Provided Provided Provided 30 minute
7 Liquid Type (Mineral oil) Provided Provided Provided 1 hour
8 Liquid Type (Mineral oil) Provided Provided Provided 2 hour
9 Liquid Type (Mineral oil) Provided Provided Provided 3 hour
10 Liquid Type (Mineral oil) Provided Provided Provided 4 hour
4a Liquid Type (Silicone oil) Provided Not provided Provided 3 hour
4b Dry Type (Dry air) Provided Not provided Provided 3 hour
7a Liquid type (Silicone oil) Provided Provided Provided 1 hour
7b Dry Type (Dir air) Provided Provided Provided 1 hour
79
7.4 Identifying the Initiating Event and the Pathway Factors
As discussed earlier in the report, the major cause of transformer failure is insulation
breakdown / arcing, which may rupture the transformer tank, releasing the oil and then
igniting the dielectric material once it is exposed to oxygen. In this research, a transformer
fire in a distribution substation is assumed to be the initial event. The pathway factors of the
event tree are developed as follow:
• Smoke detection system (SDS) - Success/ Failure
• Sprinkler system (SS) - Success/ Failure or not installed
• Manual Fire Service suppression, which is further separated into two parts:
o Firefighters’ action time (FAT): the time between when the Fire Service is
alerted and when the firefighters start to fight the fire (ta_a) is less than 10
minutes - Success/ Failure
o Manual Fire Fighting (MFF) - Success/ Failure
• Wall barrier integrity maintained (WBI) - Success/ Failure
7.5 Structuring the Event Tree Branch Logic
The structure of the event tree for transformer fires in distribution substations is shown in
Figure 7-1. The event tree logic is read off from the source (A) on the left hand side, through
the pathways (B - F) to the targets (G - J). There are two outcome segments, Yes/No, for each
pathway factors, where ‘Yes’ implies success and ‘No’ implies failure. The probability of the
various consequences is then calculated by multiplying together the various branch
probabilities of each factor. Consequence levels are measured based on the number of
fatalities (NOF) and the civilian fatality rate (CFR) (Refer to Section 7.7). In order to allow
the fire risks to be combined, the consequence are converted to equivalent monetary values
(EMV) using the value of statistical life (VSL) in Aldy and Viscusi [98]. Finally, the total risk
(J) of a transformer fire in a distribution substation is estimated by multiplying the probability
and the EMV consequence as described in Equation 7-2. A brief description for each of the
outcome events of the event tree is illustrated in Table 7-4.
80
Figure 7-1: Structure of the event tree for a transformer fire in a distribution substation Source Pathway factors Target
(A) (B) (C) (D) (E) (F) (G) (H) (I) (J) = (G)*(I)
Consequence Initiating event SDS SS FAT MFF WBI
Event No. Prob.
CFR NOF EMV
Fire risk NZD$/ fire
incident Yes Yes 1
Yes Yes 2
Yes Yes Yes 3
No
No 4
No
Yes Yes 5
No Yes 6 Transfor
mer fire No
No 7
Yes Yes 8
Yes Yes 9
No Yes Yes 10
No
No 11
No
Yes Yes 12
No Yes 13
No
No 14 where: SDS = Smoke detection system Prob. = Probability SS = Sprinkler system CFR = Civilian fatality rate
FAT = Firefighters’ action time NOF = Number of fatalities MFF = Manual fire fighting EMV = Equivalent Monetary Value WBI = Wall barrier integrity maintained
81
Table 7-4: A brief description for each of the 14 outcome events Outcome event Description of the event
1
Smoke Detection System : Success Sprinkler System : Success Firefighter Action Time : 1(See note below) Manual Fire Fighting : 1(See note below) Wall Barrier Integrity : Success
- Fire is detected by both smoke detectors and sprinkler heads;
- Early detection and fire alarm is expected; - Fire is controlled by sprinkler systems; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
2
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Success Wall Barrier Integrity : Success
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is controlled by the firefighters; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
3
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Failure Wall Barrier Integrity : Success
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is out of control; - Fire is confined to the distribution substation but
smoke may spread out of the room;
4
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Failure Wall Barrier Integrity : Failure
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is out of control and is not confined to the distribution substation;
- Outbreak fire occurred. Both fire and smoke may spread beyond the distribution substation;
5
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Success Wall Barrier Integrity : Success
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is controlled by the firefighters; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
82
Table 7-4 continued
Outcome event Description of the event
6
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Failure Wall Barrier Integrity : Success
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is out of control; - Fire is confined to the distribution substation but
smoke may spread out of the room;
7
Smoke Detection System : Success Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Failure Wall Barrier Integrity : Failure
- Fire is detected by smoke detectors; - Early detection and fire alarm is expected; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is out of control and is not confined to the
distribution substation; - Outbreak fire occurred. Both fire and smoke may
spread beyond the distribution substation;
8
Smoke Detection System : Failure Sprinkler System : Success Firefighter Action Time : 1(See note below) Manual Fire Fighting : 1(See note below) Wall Barrier Integrity : Success
- Fire is detected by the sprinkler heads; - Early detection and fire alarm is expected; - Fire is controlled by sprinkler systems; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
9
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Success Wall Barrier Integrity : Success
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is controlled by the firefighters; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
10
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Failure Wall Barrier Integrity : Success
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is out of control; - Fire is confined to the distribution substation but
smoke may spread out of the room;
83
Table 7-4 continued
Outcome event Description of the event
11
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Success Manual Fire Fighting : Failure Wall Barrier Integrity : Failure
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take action to fight the fire within 10
minutes since the Fire Service is alerted (Involvement of firefighters in the earlier stage);
- Fire is out of control and is not confined to the distribution substation;
- Outbreak fire occurred. Both fire and smoke may spread beyond the distribution substation;
12
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Success Wall Barrier Integrity : Success
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is controlled by the firefighters; - Fire may not be suppressed immediately but
confinement in the distribution substation is expected;
13
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Failure Wall Barrier Integrity : Success
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is out of control; - Fire is confined to the distribution substation but
smoke may spread out of the room;
14
Smoke Detection System : Failure Sprinkler System : Failure Firefighter Action Time : Failure Manual Fire Fighting : Failure Wall Barrier Integrity : Failure
- Fire is not detected by any fire safety systems; - No early detection and fire alarm provided; - Firefighters take more than 10 minutes to start
the fire suppression; - Fire is out of control and is not confined to the
distribution substation; - Outbreak fire occurred. Both fire and smoke may
spread beyond the distribution substation;
1 Manual Fire Service suppression is expected to be success in the case of sprinkler controlled fire
regardless the intervention time and firefighters’ ability. Hence, success or failure of the FAT and the
MFF is not considered to be necessary.
84
7.6 Quantification of the Branch Line Probabilities
7.6.1 Initiating Event Likelihood
Initiating event likelihood means the frequency of the initiating event occurring. In the
assessment, a transformer fire in a distribution substation is considered as the initiating event.
This research is particularly interested in the effects once a transformer fire occurs. To be
conservative, the likelihood of a transformer fire is assumed to be one (100%). In other words,
the event that a transformer fire has occurred in a distribution substation inside a building is
investigated.
7.6.2 Smoke Detection System (SDS)
Smoke detection systems are intended to:
1) Detect fire by smoke;
2) Provide an early warning alarm to the building occupants;
3) Alert the Fire Service;
4) Activate other fire protection systems (e.g. fire dampers and smoke exhaust systems).
Hence, good reliability of smoke detection systems can provide a reasonable level of
protection to the safety of the building occupants. It is understood that the performance of
smoke detection systems is generally high in case of transformer fires. Unlike domestic
smoke detection systems, where the system performance is often affected by lack of power
supply or delay due to the distance to the fire (as the Government of Alberta [99] stated),
smoke detection systems in distribution substations are expected to be more efficient due to
back-up power supply being provided and the room area being relatively small so the location
of smoke detectors should be close to the transformer. In an event of a liquid type transformer
fire in a distribution substation, a transformer oil fire is expected. According to the research
by Heskestad and Dobson [51], HRR and toxic smoke released by a transformer oil fire
should be large enough to activate the smoke detectors installed in the room. Hence, the
reliability of the smoke detection systems in a distribution substation is expected to be
relatively high.
85
The figure below shows the probability distribution of the performance of smoke detection
system reliability for general buildings. As stated in the Data Collection section, the reliability
data for a smoke detection system was obtained from two articles. Out of these data, a
minimum of 77.8%, a maximum of 94% and an average of 84.8% are observed. Due to the
lack of available data, a triangular distribution is considered in the assessment.
Triangular distribution (77.8%, 84.8%, 94.0%)
0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Figure 7-2: Probability distribution of the performance of smoke detection systems
Table 7-5: Summary of the probability distribution of the performance of smoke detection systems Distribution types and parameters Triangular distribution Maximum 94% Minimum 77.8% Mean 84.8%
86
7.6.3 Sprinkler System (SS)
Sprinkler systems are intended to:
1) Detect fire by hot smoke;
2) Provide an early warning alarm to the building occupants;
3) Provide an early suppression (control) to the fire;
4) Alert the Fire Service.
Sprinkler systems are known to be very effective and efficient systems to suppress or control
a fire. They activate when temperatures surrounding the sprinkler head reaches the sprinkler
activation temperature. As discussed in Section 5.2.2, a fuel load is expected in the
distribution substation, including dielectric material, electrical equipment, power cables and
the transient combustible materials. Hence, transformer fires are very unlikely to be too small
to activate the sprinkler systems as the first category in Thomas [80]. Thereforem, transformer
fires are considered to be large enough to activate the sprinkler heads unless the sprinkler
systems are defective or damaged.
The figure below shows the probability distribution of the performance of sprinkler system
reliability for general buildings. As stated in the Data Collection section, the reliability data
for a sprinkler system was obtained from a total of 11 articles. Out of these data, a minimum
of 81.3%, a maximum of 99.5% and an average of 93.4% are observed. Due to the lack of
available data, a triangular distribution is considered in the assessment.
87
Triangular distribution (81.3%, 93.4%, 99.5%)
0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Figure 7-3: Probability distribution of the performance of sprinkler system
Table 7-6: Summary of the probability distribution of the performance of sprinkler system Distribution types and parameters Triangular distribution
Maximum 99.5%
Minimum 81.3%
Mean 93.4%
88
7.6.4 Manual Fire Service Suppression – Firefighter Action Time (FAT)
The probability of the time between when the Fire Service is alerted and when the firefighters
start to fight the fire, ta_a, is less than 10 minutes (PFAT) is measured based on the results of the
NZFS FIRS statistical data analysis. According to the 20 fire incidents reported to the NZFS
FIRS with respect to fires initiating in distribution substations, the time between the Fire
Service being alerted and the firefighters starting to take action to fight the fire is often
delayed due to traffic congestion or other interventions. For example, more than half of these
fire incidents [65] have reported that the firefighters are required to wait for the power to be
isolated before they can start the fire suppression and in one case, the firefighters took almost
8 minutes in traffic.
It is understood that the earlier firefighters start attacking the fire, the higher the chance that
they can manage to control and suppress the fire. In this research, the critical time between the
Fire Service being alerted and the firefighters starting taking action to fight the fire is
considered to be 10 minutes, as Fontana et al. [100] stated. Based on the NZFS FIRS
statistical data, the probability that the Fire Service can start trying to suppress the transformer
fire within 10 minutes from receiving an alarm signal (PFAT) is examined in Table 7-7. As
defined in Section 7.2, the fire protection systems in the building are to be monitored. The
Fire Service is expected to be alerted either by a fire alarm or an emergency call.
Table 7-7: Probability that ta_a less or more than 10 minutes
Year Number of distribution
substation fires
Number of these fires that ta_a < 10
minutes
Probability of FAT
success
Probability of FAT failure
January 2000 - January 2001 4 2 50% 50%
January 2001 - January 2002 0 0 N/A N/A
January 2002 - January 2003 5 4 80% 20%
January 2003 - January 2004 4 1 25% 75%
January 2004 - January 2005 3 0 0% 100%
January 2005 - January 2006 4 2 50% 50%
89
From the available data above, it is found that the minimum, maximum and average (mean) of
the probability of FAT success are of 0%, 80% and 41%, respectively; while the minimum,
maximum and average (mean) of the probability of FAT failure are of 100%, 20% and 59%.
The following figures show the triangular distributions for the probability of success and
failure of the FAT
Triangular distribution (0%, 41%, 80%)
0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Figure 7-4: Probability distribution of FAT – success (PFAT_S)
Triangular distribution (0%, 59%, 100%)
0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Figure 7-5: Probability distribution of FAT– failure (PFAT_F)
90
Table 7-8: Summary of the probability distribution of firefighters’ action time
Probability distribution of FAT – success
(less than 10 minutes) Probability distribution of FAT – failure
(more than 10 minutes)
Distribution types and parameters Triangular distribution Triangular distribution
Maximum 80% 100%
Minimum 0% 20%
Mean 41% 59%
7.6.5 Manual Fire Service Suppression – Manual Fire Fighting (MFF)
Fontana et al. [100] state that the probability that the Fire Service can control the fire (PMFF)
depends on the ability of the firefighters and the alarm time. Based on the data found in
Fontana et al. [100], the PMFF in general buildings is estimated (Refer to Appendix D). As the
results show, the PMFF is determined to be in the range of 67.4% (volunteer non-professional
firefighters and the ta_a more than 10 minute) to 98.8% (full training professional firefighters
and the ta_a less than 10 minute). Table 7-9 shows the PMFF in different situations where the
ability of firefighters and the early warning alarm are considered.
Table 7-9: PMFF in general buildings
In general building Probability of MFF success to control the fire (PMFF_S)
Probability of MFF fail to control the fire (PMFF_F)
Firefighters’ ability
Early warning
alarm ta-a less than
10 min ta-a more than
10 min ta-a less than
10 min ta-a more
than 10 min
Professional firefighters Not provided 80.0% - 95.0% 71.6% - 85.0% 5% - 20% 5% - 29.4%
Non-professional firefighters
Not provided 75.8% - 90.0% 67.4% - 80.0% 10% - 14.2% 20% - 32.6%
Professional firefighters Provide 83.2% - 98.8% 81.1% - 96.3% 1.2% - 17.8% 3.7% - 18.9%
Non-professional firefighters
Provide 82.1% - 97.5% 71.6% - 85.0% 2.5% - 17.9% 15% - 28.4%
91
From the literature, it is found that about 9,000 firefighters are distributed over 400 fire
stations in New Zealand. The Fire Service annual report 2005 [101] states there are a total of
1607 career (professional) firefighters in New Zealand, 2005. As defined in Section 7.2, the
model building is to be located in the central city and hence is considered to be acceptable to
assume the building being protected by professional firefighters, rather the volunteer (non-
professional) firefighters. As a result, the PMFF for professional firefighters in Table 7-9 are
selected for this assessment.
Through discussion with a senior fire station officer in Victoria Fire Service [102], it is
understood that the PMFF given in Table 7-9 seem applicable in the event of general electrical
fires (e.g. dry type transformer), rather transformer oil fires, and the PMFF of transformer oil
fire should be lower. As known, oil fire can be controlled once the oil temperature is lower
than its flash point. According to the studies on the transformer dielectric fluids in Section 4.8,
it is understood that typical mineral oil and silicone oil have the minimum flash point of
100°C and 300°C, respectively. As advised by the senior fire station officer [102], the PMFF of
less flammable oil fires and flammable oil fires may reduce approximately 4 to 5% and 10 to
12%, respectively, from the PMFF of general electrical fires (Note that the mean value is used
for the assessment, i.e. the PMFF is reduced by 4.5% for less flammable oil fires and 11% for
flammable oil fires). Hence, the PMFF for different types of transformer are summarised in
Table 7-10.
Table 7-10: Probability distribution of manual fire fighting performance PMFF for different transformer types installed Smoke
Detection System (SDS)
Firefighter Action Time
(FAT)
Manual Fire Fighting
(MFF) Flammable
liquid insulated (mineral oil)
Less flammable liquid insulated
(silicone oil)
Dry type (dry air)
Success 72.2% - 87.8% 78.7% - 94.3% 83.2% - 98.8% Success
Success (less than 10
minutes) Failure 12.2% - 27.8% 5.7% - 21.3% 1.2% - 16.8%
Success 70.1% - 85.3% 76.6% - 91.8% 81.1% - 96.3% Success
Failure (more than 10 minutes) Failure 14.7% - 29.9% 8.2% - 23.4% 3.7% - 18.9%
Success 69.0% - 84.0% 75.5% - 90.5% 80.0% - 95.0% Failure
Success (less than 10
minutes) Failure 16.0% - 31.0% 9.5% - 24.5% 5.0% - 20.0%
Success 60.6% - 74.0% 67.1% - 80.5% 71.6% - 85.0% Failure
Failure (more than 10 minutes) Failure 26.0% - 39.4% 19.5% - 32.9% 15.0% - 28.4%
92
7.6.6 Wall Barrier Integrity Maintained (WBI)
The primary purposes of fire separation construction are:
1) To prevent spread of fire to other parts of the building;
2) To maintain the buildings structural integrity;
3) To provide a sufficient tenability along escape routes for some specified period of
time.
The selection of the fire resistance rating (FRR) for building construction often depends on
the fire load density, ventilation factor and conversion factor, as mentioned in the Fire
Engineering Design Guide [32]. In order to estimate the probability of the wall barrier
integrity being maintained (PWBI), it is necessary to determine the probability of the equivalent
time of fire exposure. If the equivalent time of fire exposure is over the provided FRR, the
wall barrier is considered to have failed to maintain the construction integrity. By the same
reasoning, if the provided FRR is over the equivalent time of fire exposure the wall barrier is
considered to have maintained its integrity.
The fire loads in a distribution substation containing a liquid type transformer may vary
significantly. Depending on the rupture point of the tank, the expected amount of transformer
oil released from the tank may be different. For example, if the rupture point is at the bottom
of the tank, the tank of oil is expected to be released; whereas if the rupture point is on the top
of the tank, the amount of transformer oil released from the tank is less.
Literature have indicated that tank rupture, as a result of internal transformer failure such as
arcing, is likely to occur round at the top edge of the tank. In that case, only a small amount of
the contained dielectric fluids would be expected to be released from the tank; in other words,
the fuel loads exposed in the transformer room would also be relatively low. However, no
relevant studies, researches or statistical data were found to support this phenomenon.
Therefore, to be conservative, the assessment assumes at that least half the tank of transformer
oil (50%) would be released in the case of a fire but that the transformer oil is most likely to
be released completely (100%).
93
According to a reference by ABB Power Transmission Pty Ltd. [103], it is understood that
typical dry type transformers often contain less than 5% of combustible materials compared to
the liquid type transformer. To be conservative, the fuel loads in a dry type transformer is
considered to be determined by multiplying 5% with the fuel loads in a flammable liquid
(mineral oil) insulated transformer. Hence, the probability of equivalent time of fire exposure
for dry type transformer installed can be determined.
The calculation of the equivalent time of fire exposure (te) is discussed in the C/AS1, as
follows:
Equation 7-3: fbfe wket ××=
where wf is the ventilation factor
ef is the fire load density in the design area (MJ/m2 floor area)
kb is a conversion factor
Fire load density in a distribution substation (ef):
A typical fire load density for power stations and transformer winding occupancy was found
to be 600MJ/m2 from the Fire Engineering Design Guide [32]. However, this value is given
without providing any specific details, such as the number of transformers in the station, the
power rating of the transformers, the type of dielectric material, the volume of transformer oil
or the size of transformer. Hence, a more specific fire load density for a distribution
substation containing a single 750kVA transformer is determined using the following
equations from the Fire Engineering Design Guide [32]:
Equation 7-4: f
f AEe =
Equation 7-5: ( )∑ ×=i Ci i
HME
94
Equation 7-6: )( iii VaDM ××=
where E is the total fuel load in the design area (MJ)
Af is the floor area (m2)
Mi is the mass of the fuel, i (kg)
Hc is the heat of combustion of the fuel, i (MJ/kg)
Di is the density of the fuel, i (kg/m3)
Vi is the volume of the fuel, i (m3)
a is the fraction of oil released (0.5 for 50% oil released and 1 for 100% oil
released)
i is the type of fuel
Based on the literature reviews and the site visits, it was found that the major combustible
material in a distribution substation consists of dielectric fluid (e.g. transformer oil), wood
products (e.g. wooden hardboard, furniture), electrical components and power cables (e.g.
PVC). Through discussion with a senior sales engineer [97], it is understood that a 750kVA
liquid type transformer usually contains about 550L (0.55 m3) to 840L (0.84 m3) of
transformer oil and the most likely volume of oil is about 600L (0.60 m3). In addition to the
total amount of the contained dielectric fluid in a transformer, a factor is to be introduced to
the calculation. This factor is to predict the percentage of the contained dielectric fluid is
likely to be released in the event of a fire. However, due to a lack of available information, the
conservatism is to assume that at least half the tank of transformer oil, 50% (minimum),
would be released but that the transformer oil is most likely to be released completely, 100%
(most likely value and maximum). Considering the floor area of the distribution substation is
24 m2, the volumes of the wood products and the power cables (assuming a total of 15 m of
35 mm2 and 10 m of 185 mm2 thick copper cables) are estimated to be about 0.16 m3 and
0.0024 m3, respectively. The density and heat of combustion of transformer oils are referred
to Section 4.8. Furthermore, the density and the heat of combustion for the wood products and
the power cables are found to be 720 kg/m3 and 19.8 MJ/kg and 1710 kg/m3 and 16 MJ/kg,
respectively. Table 7-11 indicates the input parameters and values for determining the fire
load density.
95
Table 7-11: Input parameters and values for determining the fire load density
Mineral oil Silicone oil Wood products
Power cables
Density, kg/m3 830 – 890 960 – 1100 720 1710
*Volume, m3 0.55 - 0.84 (0.6) 0.55 - 0.84 (0.6) 0.16 0.0024
Likelihood to be present in a transformer room in the event
of a fire (est. %)
50%- 100% (100%)
50%- 100% (100%) 100% 100%
Heat of Combustion, MJ/kg 45.9 28 19.8 16.0
*Note that the values in the brackets imply the most likely value
Ventilation factor (wf):
This factor may be calculated by knowing the dimensions of the floor area, wall/roof opening
and height of the room. The equations are shown as follow:
Equation 7-7: 5.01
)4.0(9062.00.6 43.0
>⎥⎦
⎤⎢⎣
⎡+
−⋅+⎟
⎠⎞
⎜⎝⎛=
hv
vf bH
wαα
Equation 7-8: 25.0025.0 <<= vf
vv A
A αα
Equation 7-9: 20.0≤= hf
hh A
A αα
Equation 7-10: )101(5.12 2vvvb αα −+⋅=
where H is the height of the distribution substation (m)
Av is the area of wall openings (m2)
Ah is the area of roof openings (m2)
Af is the floor area (m2)
vα is the ratio of the area of wall opening to the floor area
hα is the ratio of the area of roof opening to the floor area
In the model, the floor area of the distribution substation is defined as 24 m2, 4 m by 6 m,
with a height of 3.6 m. The size of wall openings is estimated based on the expected wall
leakage, such as cable penetrations or doorways. As defined in Section 7.2, two 1.98 m by
96
0.8 m single doors, one internal exit via the building and one direct access to the outside, are
to be installed in the distribution substation. The expected minimum wall opening is 0.1 m2
assuming there is improper sealed cable penetration or leakage through the doorways; and the
expected maximum wall opening is 3.2 m2 assuming both the single doors are fully opened in
the case of a fire. However, it is considered to be very likely to have both doors fully opened
in an event of a transformer fire and it is known the smaller the wall openings, the higher the
ventilation factor and the higher the equivalent time of fire exposure would be. Therefore, to
be conservative, the most likely wall opening is assumed to be 0.5 m2; one single door
partially opened during fire.
Due to the general restriction of openings on the roof in a distribution substation, the roof
openings are likely to be small. However, small leakages may occur due to improper sealed
cable penetrations and the venting system where the automatic fire damper may be defective
or not installed. Therefore, the area of roof opening is assumed to be in the range of 0.01 m2
and 0.1 m2 and is a uniform distribution. Table 7-12 indicates the input parameters and values
for determining the ventilation factor.
Table 7-12: Input parameter and values for determining the ventilation factor Floor area (m2) 24
Height of roof (m) 3.6
Area of wall openings (m2) Triangular distribution 0.1 – 3.2 (0.5)
Area of roof openings (m2) Uniform distribution 0.01 – 0.1
Conversion factor (kb):
Conversion factor is determined based on the use of the construction materials in the
distribution substations. By knowing the thermal inertia (kρc) of the distribution substation
construction materials, the conversion factor can be found from the table given in the Fire
Engineering Design Guide [32]. For a high-rise building, 21.6m high, the building is
generally constructed with concrete, but in some cases brick and masonry may be used
instead. Because selection of the construction materials may vary in different buildings, the
construction material is not defined in this study. Instead, sensitivity analysis was carried out
to analysis the effects of the conversion factor on the overall results of the equivalent time
calculation using the @Risk4.5.
97
As a result of the sensitivity analysis, it was found that conversion factor may change the
result of equivalent time of fire exposure by about 25% to 25.7%, depending on the type of
insulation fluid and the construction materials installed. This change is considered to be
significant in the measurement of the equivalent time. Therefore, a range of thermal inertia is
used to cover the thermal inertia of three possible construction materials (concrete, brick and
masonry). Uniform distribution is used for the conversion factor with the boundaries of 0.065
(lightweight concrete ceiling and floor, plasterboard walls) and 0.08 (Normal concrete ceiling
and floor, plasterboard walls). Note the values of thermal conductivity (k), density (ρ) and
specific heat (c) for these construction materials are found from Karlsson [104].
Overall, the equation for the equivalent time can be rewritten by substituting Equation 7-8
through Equation 7-10 into Equation 7-7, as follows:
Equation 7-11:
( ) ( ) ( )[ ]cablecablecablewoodwoodwoodoiloiloilf
fbe HcVDHcVDHcVaD
Awk
t ⋅⋅+⋅⋅+⋅⋅⋅⋅×
= )(
Due to the involvement of the probability distributions as listed in Table 7-13, the equivalent
time of fire exposure (te) is determined using @Risk4.5. Using a trial-and-error method, the
result is found to have no significant differences when the number of iterations is above 5,000.
Table 7-13: The input probability distributions for the calculation of equivalent time Probability distribution
Input parameters Unit Distribution types Min.
valueMost likely
value Max. value
Area of wall openings (Av) m2 Triangular distribution 0.1 0.5 3.2
Area of roof openings (Ah) m2 Uniform distribution 0.01 Not required 0.1 Density of mineral oils (Doil) kg/m3 Uniform distribution 830 Not required 890 Density of silicone oils (Doil) kg/m3 Uniform distribution 960 Not required 1100 Total volume of the oil contain (Voil) m3 Triangular
distribution 0.55 0.60 0.84
Est. % of oil to be released from a transformer in the event of a fire ----- Triangular
distribution 0.50 1.0 1.0
Conversion factor (kb) ----- Uniform distribution 0.65 Not required 0.08 * Most likely value is not required for Uniform distribution.
98
The probability of the wall barrier integrity being maintained (PWBI) can be determined based
on the probability distribution of the equivalent time of fire exposure. Several standard FRR
constructions are selected to be assessed, such as FRR of 30 minute, 1 hour, 2 hour, 3 hour
and 4 hour. These FRR levels are considered as the critical time for the wall barrier to
maintain its integrity. In other words, when the equivalent time exceeds the critical time of the
selected standard FRR, the wall barrier is considered to fail.
A summary of the overall results is shown in Table 7-14.
D istribution for M /E41
Val
ues
in 1
0 -3
0
1
2
3
4
5
6
7
8
9
M ean=163.8573
0 70 140 210 280 350
@ RISK Student V ersionFor A cademic U se Only
240.4945240.4945240.4945240.4945
0 70 140 210 280 350
5% 90% 5% 97.31 240.4945
M ean=163.8573 M ean=163.8573
Figure 7-6: Probability distribution of equivalent time for transformer with mineral oil
S – PWBI_S (success) F – PWBI_F (failure)
30 min
S: 0 % F: 100%
S: 0% F: 100%
1 hr 2 hr 3 hr 4 hr
S: 18% F: 82%
S: 64% F: 36%
S: 95% F: 5%
99
Distribution for S/F41
0.000
0.002
0.003
0.005
0.007
0.009
0.010
0.012
M ean=123.9843
0 100 200 300
@ RISK Student V ersionFor A cademic U se Only
00
0 100 200 300
5% 90% 5% 74.1263 180.5325
0 100 200 300
M ean=123.9843
Figure 7-7: Probability distribution of equivalent time for transformer with silicone oil
As ABB Power Transmission Pty. Ltd. [103] stated, typical dry type transformer often contain
less than 5% of combustible materials compared to the liquid type transformers. To be
conservative, the fuel loads in a dry type transformer is considered to be determined by
multiplying 5% with the fuel loads in a flammable liquid (mineral oil) insulated transformer.
Therefore, the probability of equivalent time of fire exposure for dry type transformer
installed is determined as follows:
30 min 1 hr 2 hr 3 hr 4 hr
S: 0 % F: 100%
S: 1% F: 99%
S: 48% F: 52%
S: 95% F: 5%
S: 99.9% F: 0.1%
S – PWBI_S (success) F – PWBI_F (failure)
100
D istribution for D/G41
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
M ean=23.31891
0 10 20 30 40 50
@ RISK Student V ersionFor A cademic U se Only
5050
0 10 20 30 40 50
5% 90% 5% 14.8402 31.8609
0 10 20 30 40 50
M ean=23.31891
Figure 7-8: Probability distribution of equivalent time for transformer with dry type dielectric material
Table 7-14: Summary of the probability distribution of wall barrier integrity maintained (PWBI)
FRR construction WBI
Flammable liquid insulated transformer installed (mineral oil)
Less flammable liquid insulated transformer installed (silicone oil)
Dry type transformer
installed (dry air)
Success 0% 0% 89% 30 minute
Failure 100% 100% 11%
Success 0% 1% 100% 1 hour
Failure 100% 99% 0%
Success 18% 48% 100% 2 hour
Failure 82% 52% 0%
Success 64% 95% 100% 3 hour
Failure 36% 5% 0%
Success 95% 100% 100% 4 hour
Failure 5% 0% 0%
S: 89 % F: 11 %
30 min
S: 100 % F: 0 %
> 1 hr
S – PWBI_S (success) F – PWBI_F (failure)
101
7.6.7 Summary of the Probability Distributions for the Pathway Factors
An overall summary of the probability distributions for the pathway factors in each scenario
with a short description are shown in Table 7-15. The incident outcomes in each scenario are
classified into four groups as follows:
Group 1) Sprinkler systems success: This is the best case scenario. The sprinkler systems are
in service and operating as intended in the event of a fire. Sprinkler heads, as a thermal
detection system, are expected to detect the fire as well as providing an early suppression to
control fire spread. Hence, the loss expectancy is considered to be normal. Occupants are
expected to escape with no injuries. Fire damage to the object of origin is expected.
Group 2) Sprinkler systems fail but manual Fire Service suppression is a success: This
situation is considered as a selected probable case. In this case, the sprinkler system is
defective, fails to operate or is just not installed in the first place, but the firefighters are able
to control the fire. However, the fire may spread to other parts of the room. The probable
maximum loss is expected and the fire damage to parts of the room shall be addressed. Life
safety is not considered to be significant in this situation. No injuries are expected.
Group 3) Both automatic and manual suppression measure fail but the fire is successfully
confined to the room of origin: This situation is considered as a selected probable case. The
probable maximum loss is expected and the fire damage to the entire room of origin shall be
addressed. Life safety is addressed in this case.
Group 4) All fire safety protection systems fail (uncontrolled fire), which is the worst case
scenario: All detection and protection features are assumed to be out of service or ineffective
and the FRR construction fails to limit the fire to the room. Hence, maximum foreseeable loss
is expected and fire damage beyond the room of origin may occur. Health and life safety may
be threatened.
102
Table 7-15: Overall summary of the probability distributions for the pathway factors
Pathway factor Description Relevant
scenarios Success 1Failure
SDS (Refer to
Section 7.6.2)
System installed, the probability of the system reliability is expressed as a triangular distribution
All scenarios
Triangular distribution (0.78, 0.85,
0.94)
Triangular distribution
(0.06, 0.15, 0.22)
System not installed Scenario
1 – 5, 4a, 4b 0% 100%
SS (Refer to
Section 7.6.3) System installed, the probability of the system reliability is expressed as a triangular distribution
Scenario 6 – 10, 7a, 7b
Triangular distribution
(0.81, 0.93, 1)
Triangular distribution
(0, 0.07, 0.19)
FAT (Refer to
Section 7.6.4)
The time between the Fire Service being alerted and the firefighters starting to take action to fight the fire (ta_a) is less than 10min. Triangular distribution is obtained for the probabilities based on the NZFS FRIS data. This factor is appropriate for all scenarios.
All scenarios Triangular distribution
(0, 0.41, 0.8)
Triangular distribution
(0.2, 0.59, 1)
1 Note that sum of the success and failure probability for the same factor should be equal to
one. To avoid confliction occur (success and failure probability for a same factor do not equal
to one) while the Monte Carlo simulation, the probability distribution of success is used in the
simulation and the probability of failure is simply equal to one minus the probability of
success, i.e. P (failure) = 1 - P (Success). However, the probability distributions of failure are
given for reference.
103
Table 7-15 continued
Pathway factor Description Relevant
scenarios Success 1 Failure
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10
Uniform distribution (0.72, 0.88)
Uniform distribution (0.12, 0.28)
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 4a, 7a
Uniform distribution (0.79, 0.94)
Uniform distribution (0.06 0.21)
Case 1: SDS success FAT success
c) Dry type transformer (Dry air)
Scenario 4b, 7b
Uniform distribution (0.83, 0.99)
Uniform distribution (0.01, 0.17)
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10
Uniform distribution (0.70, 0.85)
Uniform distribution (0.15, 0.30)
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 4a, 7a
Uniform distribution (0.77, 0.92)
Uniform distribution (0.08, 0.23)
Case 2: SDS success FAT failure
c) Dry type transformer (Dry air)
Scenario 4b, 7b
Uniform distribution (0.81, 0.96)
Uniform distribution (0.04, 0.19)
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10
Uniform distribution (0.69, 0.84)
Uniform distribution (0.16, 0.31)
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 4a, 7a
Uniform distribution (0.76, 0.91)
Uniform distribution (0.09, 0.24)
Case 3: SDS failure FAT success
c) Dry type transformer (Dry air)
Scenario 4b, 7b
Uniform distribution (0.80, 0.95)
Uniform distribution (0.05, 0.20)
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10
Uniform distribution (0.61, 0.74)
Uniform distribution (0.26, 0.39)
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 4a, 7a
Uniform distribution (0.67, 0.81)
Uniform distribution (0.19, 0.33)
2 MFF (Refer to
Section 7.6.5)
Case 4: SDS failure FAT failure
c) Dry type transformer (Dry air)
Scenario 4b, 7b
Uniform distribution (0.72, 0.85)
Uniform distribution (0.15, 0.28)
2 Note that all four cases are expected to be used in all scenarios. The difference between the
four cases is a combination of early earning system (i.e. SDS) and the intervention time (i.e.
FAT). These events are expected in each of the scenarios and; therefore, all four cases are to
be used in the assessment for each scenario.
104
Table 7-15 continued
Pathway factor Description Relevant
scenarios Success 1Failure
Case 1: Construction having a FRR of 30 minute
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10 0% 100%
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10 0% 100%
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 7a 1% 99%
Case 2: Construction having a FRR of 1 hour
c) Dry type transformer (Dry air)
Scenario 7b 100% 0%
Case 3: Construction having a FRR of 2 hour
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10 18% 82%
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10 64% 36%
b) Less flammable liquid insulated transformer (Silicone oil)
Scenario 4a 95% 5%
Case 4: Construction having a FRR of 3 hour
c) Dry type transformer (Dry air)
Scenario 4b 100% 0%
3 WBI (Refer to Section 7.6.6)
Case 5: Construction having a FRR of 4 hour
a) Flammable liquid insulated transformer (Mineral oil)
Scenario 1 – 10 95% 5%
3 Note that only construction having a FRR of 1 hour and 3 hour is further assessed in
Scenario 7a and 7b and Scenario 4a and 4b with different transformer types. Hence, the PWBI
for these scenarios are also included in the table above.
105
7.7 Quantification of the Consequence
7.7.1 Introduction
Consequence of fire can generally be categorized into one of the followings:
• Property damage
• Life safety exposure
• Business interruption
• Environmental impact
However, for the purpose of this research, only the life safety exposure is examined as
consequences in fire. To determine the life safety consequence, two significant parameters are
considered. These are the rates of civilian fatalities and injuries in fire and the value of
statistical life (VSL).
7.7.2 Rate of civilian fatalities and injuries
In this chapter, the rate of civilian fatalities and injuries for each outcome event from the
event tree analysis are determined based on the effectiveness of various combinations of fire
safety systems in the building. This approach has also been introduced in Thomas [80].
Thomas [80] has studied the effectiveness of several fire safety systems in fires reported to
the NFIRS between 1983 and 1995. In the study, it compared the consequence of fires for the
various occupancies and with the various combinations of sprinkle, detector and FRR
construction presence with respects to the number of fire fighter and civilian casualties and
estimated property losses. The effectiveness of sprinkler, detector and FRR construction in
reducing death and injury for residential apartments and retails is extracted from Thomas [80]
and reproduced in Table 7-16.
Note that in comparison with the life safety consequence of distribution substation fires
between 1980 and 2002 reported to the NFIRS as indicated in Table 5-1 (2.1 to 2.8 fatalities
per 1000 fire and 39 to 57 injuries per 1000 fire), the rate of casualties in Thomas study is
106
considered to be more conservative (2.8 to 11 fatalities per 1000 fire and 90 to 117 injuries
per 1000 fire).
Table 7-16: Rate of casualties in residential apartment and retail areas with various combinations of fire safety systems
Detector Sprinkler FRR construction
Rate of civilian fatalities per
1000 fires
Rate of civilian injury per 1000
fires
Present Present Present 2.8 90.4
Present Absent Present 6.8 109.4
Present Absent Absent 8.7 116.8
Absent Present Present 3.7 76.8
Absent Absent Present 8.3 95.5
Absent Absent Absent 11 102.6
The total rates of civilian fatalities and injuries per fire for each outcome event from the Event
Tree Analysis are shown in Table 7-17. As expected, in the event of sprinkler or MFF control
fire, the FRR construction is considered to be able to withstand the fire; therefore, the rate of
casualties of Event 2 is assumed to be equal to Event 3 (also applies to Event 5 / Event 6,
Event 9 / Event 10 and Event 12 / Event 13).
Moreover, the pathway factor of FAT is expected to affect the probability of manual fire
fighting (MFF) only and it was included during the likelihood calculation, and therefore, the
civilian fatality rate of Event 2 is assumed to be equal to Event 5 (also applies to Event 3 /
Event 6, Event 4 / Event 7, Event 9 / Event 12, Event 10 / Event 13 and Event 11 / Event 14)
107
Table 7-17: Rate of casualties per fire in the model building with various combinations of fire safety systems for each outcome event.
Initiating event SDS SS FAT MFF WBI Event
No. Rate of civilian fatality per fire
Rate of civilian injury per fire
Yes Yes 1 2.8 x 10-3 90.4 x 10-3 Yes Yes 2 6.8 x 10-3 109.4 x 10-3 Yes Yes Yes 3 6.8 x 10-3 109.4 x 10-3 No No 4 8.7 x 10-3 116.8 x 10-3 No Yes Yes 5 6.8 x 10-3 109.4 x 10-3
No Yes 6 6.8 x 10-3 109.4 x 10-3 Transformer fire No
No 7 8.7 x 10-3 116.8 x 10-3 Yes Yes 8 3.7 x 10-3 76.8 x 10-3 Yes Yes 9 8.3 x 10-3 95.5 x 10-3 No Yes Yes 10 8.3 x 10-3 95.5 x 10-3 No No 11 11.0 x 10-3 102.6 x 10-3 No Yes Yes 12 8.3 x 10-3 95.5 x 10-3 No Yes 13 8.3 x 10-3 95.5 x 10-3 No No 14 11.0 x 10-3 102.6 x 10-3
108
7.7.3 Value of statistical life To estimate the total risk of a transformer fire, these outcome events must have a common
unit. One typical way is to translate the outcome event into the equivalent monetary value
(EMV). From the literature review, it is understood that the approach of placing a value on
casualties in fire has been questioned by relevant stakeholders. However, Office of the
Deputy Prime Minister (ODPM) [105] and Ashe W. et al. [106] have indicated that indeed,
such values are implicit in decision made for many organizations, in particular for Department
of Transport (e.g. decision on whether to fund a road improvement), Department of Fire
Service (e.g. how much to spend on the fire protection systems versus the life safety
consequence) as well as the medical insurance companies and the like.
In addition, Krupnick [107] also stated that the value of statistical life (VSL) is an expression
of the preference of reducing the risk of death (in monetary terms). Therefore, in this research,
the civilian fatalities and injuries are to be translated to an equivalent monetary value (EMV)
for the cost-benefit analysis.
Depending on the age group, educational qualification and wealth, the value of a statistical
life in 2002 to 2006 is found to be in a range of NZD $1.9 million and NZD $15million from
ODPM [105] (United Kingdom), Ashe [106] (Australia), Slayter [108] (Australia), Danish
Emergency Management Agency (DEMA) [109] (Denmark), Ministry of Transport [110]
(New Zealand), Aldy and Viscusi [98] (USA), Krupnick [107] (USA) and a text book, Barry
[93] (USA). Considering these studies, the values used in this research are $3 million for the
value of a fatality and $ 250,000 for the value of an injury.
109
7.7.4 Consequence of a fire
As the result, the life safety consequence of all 14 outcome events is translated to an EMV as
indicated in Table 7-18.
Table 7-18: EMV for the life safety consequence of each outcome events
Event No.
Rate of civilian fatality per fire
Value of a fatality
Rate of civilian injury per fire
Value of an injury
Equivalent Monetary Value
(EMV) NZD$
1 0.0028 $3,000,000 0.0944 $250,000 $32,000
2 0.0068 $3,000,000 0.1094 $250,000 $47,750
3 0.0068 $3,000,000 0.1094 $250,000 $47,750
4 0.0087 $3,000,000 0.1168 $250,000 $55,300
5 0.0068 $3,000,000 0.1094 $250,000 $47,750
6 0.0068 $3,000,000 0.1094 $250,000 $47,750
7 0.0087 $3,000,000 0.1168 $250,000 $55,300
8 0.0037 $3,000,000 0.0768 $250,000 $30,300
9 0.0083 $3,000,000 0.0955 $250,000 $48,775
10 0.0083 $3,000,000 0.0955 $250,000 $48,775
11 0.0110 $3,000,000 0.1026 $250,000 $58,650
12 0.0083 $3,000,000 0.0955 $250,000 $48,775
13 0.0083 $3,000,000 0.0955 $250,000 $48,775
14 0.0110 $3,000,000 0.1026 $250,000 $58,650
110
7.8 Fire Risk Estimation
Risk estimation is a process for assigning the frequencies and consequences of the hazardous
event into various levels of risk. It can be expressed in terms of the likelihood of incident
outcomes (outcomes probability) and the consequences (translated into the EMV) as
illustrated in Equation 7-2. The probability distributions for each of the pathway factors have
been introduced in Section 7.6.2 through to Section 7.6.6. Based on these defined probability
distributions, Monte Carlo simulations for the fire risk estimation were conducted using
@Risk4.5 as discussed in Section 7.1. In the simulations, the settings generally follow the
default choice except for the sampling type and the number of iterations.
In the simulations, “Monte Carlo” is selected as the type of sampling. For the number of
iterations, a trial-and-error method is used. It is found that the results would have no
significant differences when the number of iterations rises above 5,000. Hence, 5,000
iterations are considered to be sufficient for the simulation. A summary of the statistical
values of the total risk (NZD$/ fire incident) for each scenario is shown in Table 7-19 (Refer
to Appendix E).
Note that this research primarily assumed that the fire protection required by the compliance
document (C/AS1) is considered as the minimum requirements in the assessment, such as
installing smoke detection and alarm systems and a minimum of 30 minute fire separation
between the distribution substation and the interior spaces of the building. Scenario 1, which
has the minimum fire protection requirements, is expected to have the highest risk compared
to other scenarios.
111
Table 7-19: summary of the statistical values of the total risk (NZD$/fire incident) for each scenario
Total risk: NZD$/ fire incident Re (existing risk of the base case) or Rm (modified risk of the alternative)
Mean Standard
Deviation 5% tile 95% tile Min Max
Scenario 1 (Base case 1) 49,690 240 49,310 50,080 49,013 50,450
Scenario 2 49,690 240 49,310 50,080 49,010 50,450
Scenario 3 49,330 190 49,030 49,650 48,780 49,950
Scenario 4 48,620 100 48,450 48,790 48,310 48,960
Scenario 5 47,990 40 47,920 48,050 47,890 48,090
Scenario 6 32,520 710 31,440 33,800 30,990 34,460
Scenario 7 32,520 710 31,440 33,800 30,990 34,460
Scenario 8 32,490 700 31,430 33,740 30,990 34,380
Scenario 9 32,420 670 31,400 33,620 30,980 34,210
Scenario 10 32,370 650 31,390 33,530 30,980 34,060
Scenario 4 (Base case 2) 48,620 100 48,450 48,790 48,310 48,960
Scenario 4a 47,960 40 47,900 48,030 47,850 48,070
Scenario 4b 47,900 30 47,840 47,950 47,810 47,980
Scenario 7 (Base case 3) 32,520 710 31,440 33,800 30,990 34,460
Scenario 7a 32,470 690 31,480 33,700 30,990 34,300
Scenario 7b 32,360 640 31,380 33,510 30,980 34,040
Mean Min Max 95% tile5% tile
112
As a result of the Monte Carlo simulation, the sensitivity to the total risk is also obtained. As
the result, it is found that active fire safety systems, such as smoke detection systems and
sprinkler systems, are the most sensitive parameters. In particular, when a sprinkler system is
presented in the building (Scenario 6 to Scenario 10), it is always the most sensitive factor.
113
CHAPTER 8 COST-BENEFIT ANALYSIS
8.1 Introduction to Cost-Benefit Analysis
Cost-benefit analysis is a practical way of evaluating the economic efficiency of resource
allocation. By analysing the cost requirement for the risk reduction alternatives and
determining the benefit cost ratio (B/C), the mutually exclusive scenarios may have a
common unit so that they can be compared and ranked in accordance to their priorities. As a
result, the economically best investment can be found. Overall, the information provided from
the B/C analysis may include:
• The estimated equivalent monetary value of the fire risk reduction
• The initial and annual cost of the alternatives
• The B/C ratio
Any alternative scenario with a B/C ratio above one is considered to be a beneficial
investment. In addition to the B/C analysis, the effectiveness and efficiency of the alternative
scenarios are also discussed in this study. Since the main concern of this study is the health
and safety impacts on people (life safety consequences), the benefit of the risk reduction
alternatives primarily apply to the building occupants. Note that loss of property (impact on
property), business interruption costs (impact on the retail shops) and environmental damage
are excluded from this assessment.
In this chapter, the 14 scenarios are analysed based on three critical base scenarios. A scenario
with the lowest level of fire protection (Scenario 1) is considered as the base case for Scenario
2 – Scenario 10, where a flammable liquid (mineral oil) insulated transformer is used. The
purpose of this part of the analysis is to evaluate the cost and benefit of different fire safety
designs without the influence of different transformer types.
114
Thereafter, Scenario 4 and Scenario 7 are selected as the base cases for Scenario 4a and 4b
and Scenario 7a and 7b, respectively. The purpose of this part of the analysis is to evaluate the
cost and benefits of different types of transformers, such as less flammable liquid (silicone oil)
insulated transformers and dry type (dry air) transformers. The reason for selecting Scenario 4
and Scenario 7 as the base cases in this part is due to the fire safety designs in these two
scenarios being recommended in the NFPA as mentioned in Table 3-5. Note that NFPA is the
only standard provided the fire protection requirements for other types of transformers.
115
8.2 Methodology
According to the benefit cost analysis manual [111], the benefit cost ratio (B/C) can be
measured by the total discounted benefits divided by the total discounted costs. In general, it
is a beneficial investment if the B/C ratio is greater than one. The factors of the B/C ratio
include:
The existing risk estimated for the base case;
The modified risk estimated for the alternatives;
Initial cost of the alternatives;
Annual cost of the alternatives;
The present worth factor which is a function of the interest rate;
The estimated useful lifetime of the system.
The following equations are extracted from the benefit cost analysis manual [111] to
determine the B/C ratio:
Equation 8-1: ( )
CINiAPACB ,,// = Equation 8-2: CB ARA −=
Equation 8-3: meB RRR −= Equation 8-4: ( ) ( )( )N
N
iiiNiAP+⋅
−+=
111,,/
where B/C is the benefit cost ratio
A is the cost avoidance ($)
IC is the initial cost ($)
AC is the annual cost ($)
RB is the risk benefit ($)
Re is the existing estimate risk ($)
Rm is the modified estimate risk ($)
P/A is the present worth factor
i is the interest rate (%)
N is the useful lifetime (year)
116
In the following section, both initial and annual costs of individual systems or equipment are
provided with a distribution to capture the uncertainty in the values. However, only the mean
value is used to determine the B/C ratio.
For the calculation, the annual interest rate (7%) is assumed to be constant throughout the
useful lifetime of the distribution substation (30 years). The value of the annual interest rate is
obtained by averaging the annual interest rate from different banks in New Zealand in 2006.
As introduced by Tremblay [69], Guy [112] and ABB Power Transmission [113], an average
useful lifetime of 30 years is considered to be appropriate for the major equipment in
distribution substations, such as transformers and switchgear. As a result, the present worth
factor (P/A, i, N) is determined to be 12.41 using Equation 8-4.
117
8.3 Cost Analysis for the Risk Reduction Alternatives
8.3.1 Cost Consideration
Costs of alternative scenarios can be expressed in terms of their initial costs and annual costs.
In this study, initial costs are defined as the cost incurred during the first year from the system
being installed, whilst annual costs are the ongoing operating costs for maintenance and
rehabilitation of the system. The initial costs can be determined by the sum of two separate
costs; these are:
System (equipment) costs;
Installation (labour) costs.
It is understood that the installation costs are very difficult to predict because it can vary
significantly depending on the individual case. Rawlinsons 2004 [114] has proposed an
allowance of 5% to 10% on top of the equipment costs is considered to be appropriate for the
total initial costs. In addition, the cost of the individual equipment or systems are measured
based on the values given in Rawlinsons 2004 [114].
On the other hand, the annual costs are the ongoing costs. These costs may include the
following:
Maintenance costs (e.g. cleaning for dry type transformers);
Inspection and testing costs (e.g. sprinkler heads, detectors);
Ongoing operating costs (e.g. transmission connection, on-duty observers);
Replacement costs (e.g. oil replacements).
The cost estimates for individual equipment or systems are discussed in the following sections.
Note that, smoke detection system is considered to be a common system for all scenarios;
therefore, no additional costs are required from the base case. Hence, the costs estimates for
the smoke detection system are not discussed in the analysis.
118
8.3.2 Sprinkler System
As defined previously, the model building is not protected with sprinkler systems. Therefore,
if sprinkler systems are installed in a distribution substation, the total cost of the sprinkler
systems should include the cost of sprinkler heads, control board, pipes, fittings, valves and
the like. It is understood that in sprinklered buildings, sprinkler system is likely to be
extended to the distribution substation inside and the costs of this extension is expected to be
low. Therefore, the cost-effectiveness of installing a sprinkler system in the distribution
substation inside a sprinklered building is expected to be higher than installing a sprinkler
system in the distribution substation inside a non-sprinklered building due to its low cost. To
be conservative, this research only assesses the risk of transformer fire in a non-sprinklered
building. Hence, the costs of control board, valves and the like are included in the assessment.
It is understood that typical high-rise non-sprinklered buildings generally contain two
individual main pipes from the main water supply: one is for the building use and another one
is for fire hydrants. If sprinkler systems are installed, an additional main pipe is required for
supporting the sprinkler systems separately from another two main pipe. However, through
discussion with a fire service engineer [115], it is understood that the additional main pipe for
the sprinkler systems may not be necessary to the model building in this assessment. It is due
to the required water flow to the sprinkler heads in the distribution substation on ground floor
being able to be supported by the fire hydrant pipe.
In the model building, the distribution substation is located on the ground floor of the building.
The floor area is 24 m2 with floor-to-ceiling height of 3.6 m. As mentioned, the water supply
to the sprinkler heads is from another main pipe (fire hydrant). Figure 8-1 shows typical
sprinkler systems and associated equipment for distribution substations. As stated in Standard
NZS 4541:2003 [33], each sprinkler head can provide a coverage of 3 m by 4 m (12 m2).
However, due to the shape of the distribution substation, three sprinkler heads are required to
provide a full coverage to the area. The associated equipment of the sprinkler systems
includes a gate valve, a monitored valve, an inspectors connection and the Fire Service
connection, as discussed by Puchovsky [116].
119
Figure 8-1: Basic components of the sprinkler systems in the distribution substation
According to Standard NZS 4541:2003 [33], the required water discharge density for liquid
type and dry type transformers is at least 10 mm/min and 5 mm/min, respectively. As known,
higher water discharge densities usually require larger pipe sizes, valves and fittings.
Therefore, the cost of sprinkler systems for liquid type transformers is expected to be higher
than the dry type transformers.
The total cost of the sprinkler systems for a distribution substation with different types of
transformers, in the model building, has been evaluated by the fire service engineer [115].
Considering that the water flow and pressure of the existing fire hydrant pipe is sufficient to
support the sprinkler systems (no pumps are required), a conservative total cost of the
sprinkler systems are estimated to be in the range of NZD$10,000 to NZD$14,000 for
distribution substations with a liquid type transformer and NZD$9,000 to NZD$13,000 for
distribution substations with a dry type transformer. Note that the given costs have included
the installation costs.
4m
6m
3.6m
2m 2m
(1) Pipe for Building Use (2) Pipe for Fire hydrant (3) Pipe for sprinkler system (4) Gate valve to control water
supply to system (5) Monitored valve and flow
switch (6) Fire dept. connection (7) Control board (8) Inspector’s test connection (9) Sprinkler head
Main water supply
(1) (2) (3)
(5)
2m
2m 1m 1m
(9) (9) (9)
(3) (4)
(6)
(8) (7)
120
The frequency of the sprinkler systems inspection and testing are covered by Standard AS
1851:2005 [117]. For different parts of the system, the required inspection and testing may
vary from once a year to as much as once a week. For instance, the sprinkler system interface
control valves are required to be inspected weekly while the alarm valve is to be inspected
yearly.
Through discussion with a senior fire protection engineer [118], the annual inspection and
testing cost is estimated to be in the range of NZD$400 to NZD$600 (including weekly
inspection and testing). On the other hand, the cost of the transmission connection to on-duty
observer is advised to be about NZD$200 to NZD$300. In addition, the replacement cost is
assumed to be in the range of NZD$0 to NZD$200 per year which may include the cost of
sprinkler heads, fitting and the like. Table 8-1 shows the cost of sprinkler systems in a
distribution substation and a summary of the initial costs and annual costs are indicated in
Table 8-2.
Table 8-1: Cost of sprinkler systems in the distribution substation Description Cost (NZD$)
System/ Installation cost Sprinkler systems for distribution substation with a liquid oil insulated transformer $10,000 - $14,000
Inspection and testing cost Expert engineer justified $400 - $600 pa
On-going operation cost Transmission connection to on-duty observer $200 - $300 pa
Replacement cost General equipment (e.g. sprinkler heads) $0 - $200 pa
System/ Installation cost Sprinkler systems for distribution substation with a dry type transformer $9,000 - $13,000
Inspection and testing cost Expert engineer justified $400 - $600 pa
On-going operation cost Transmission connection to on-duty observer $200 - $300 pa
Replacement cost General equipment (e.g. sprinkler heads) $0 - $200 pa
Table 8-2: Initial costs and annual costs of sprinkler systems Initial cost (NZD$) Annual cost (NZD$) Relevant
scenarios Transformer type Min. Mean Max. Min. Mean Max.
Scenario 1~5, 4a Liquid oil type $0 $0 $0 $0 $0 $0
Scenario 6~10, 7a Liquid oil type $10,000 $12,000 $14,000 $600 $850 $1,100
Scenario 4b, 7b Dry type $9,000 $11,000 $13,000 $600 $850 $1,100
121
8.3.3 Fire Resistance Rated Constructions (Wall barrier)
The cost of the FRR construction is determined based on the area of interior walls and the fire
doors in the distribution substation. In this case, the total area of interior walls is determined
to be 68.8m2 (subtract the area of the fire doors). The cost of the fire walls and doors are
found in Rawlinsons 2004 [114]. As mentioned previously, the labour cost is to be 5% to 10%
of the equipment cost.
As expected, FRR construction has a very high reliability. According to Standard
AS 1851:2005 (Table 17.4.1.1: Fire and Smoke barriers – walls) [117], fire construction is
required to be inspected once every half year (e.g. check of penetrations and dampers). The
maintenance, inspection and testing costs are provided by Integrity Fire Protection. An
inspection cost of NZD$300 to NZD$600 is estimated. Hence, the cost of the FRR
constructions and a summary of the initial costs and annual costs of the FRR construction
system are shown in Table 8-3 and Table 8-4, respectively.
Table 8-3: Cost of the FRR constructions
Description Cost (NZD$)
FRR wall: ($128/m2 - $136/m2) * 68.8m2 $8,800 - $9,400 System cost
Fire Door: $1,150 each (for two doors) $2,300
Installation cost 5% - 10% of the system costs $560 - $1,170
30 min
Inspection and testing cost Expert engineer justified $300 - $600 pa
FRR wall: ($132/m2 - $142/m2) * 68.8m2 $9,000 - $9,800 System cost
Fire Door: $1,350 each (for two doors) $2,700
Installation cost 5% - 10% of the system costs $590 - $1,250 1 hr
Inspection and testing cost Expert engineer justified $300 - $600 pa
FRR wall: ($157/m2 - $170/m2) * 68.8m2 $10,000 - $11,700 System cost
Fire Door: $1,500 each (for two doors) $3,000
Installation cost 5% - 10% of the system costs $590 - $1,470 2 hr
Inspection and testing cost Expert engineer justified $300 - $600 pa
122
Table 8-3 continued
Description Cost (NZD$)
FRR wall: ($159/m2 - $168/m2) * 68.8m2 $10,900 - $11,700 System cost
Fire Door: $1,750 each (for two doors) $3,500
Installation cost 5% - 10% of the system costs $720 - $1,520 3 hr
Inspection and testing cost Expert engineer justified $300 - $600 pa
FRR wall : ($173/m2 - $205/m2) * 68.8m2 $11,900 - $ 14,100 System cost
Fire Door : $2,100 each (for two doors) $4,200
Installation cost 5% - 10% of the system costs $805 - $1,830
4 hr
Inspection and testing cost Expert engineer justified $300 - $600 pa
Table 8-4: Initial costs and annual costs of the FRR construction Initial cost (NZD$) Annual cost (NZD$)Relevant
scenarios Description Min. Mean Max. Min. Mean Max.
Scenario 1, 6 30 minute FRR: total FRR wall area = 68.8m2, two single doors $11,700 $12,300 $12,900 $300 $450 $600
Scenario 2, 7, 7a, 7b
1 hour FRR: total FRR wall area = 68.8m2, two single doors $12,300 $13,100 $13,800 $300 $450 $600
Scenario 3, 8 2 hour FRR: total FRR wall area = 68.8m2, two single doors $13,700 $15,400 $16,200 $300 $450 $600
Scenario 4, 9, 4a, 4b
3 hour FRR: total FRR wall area = 68.8m2, two single doors $15,100 $16,000 $16,700 $300 $450 $600
Scenario 5, 10 4 hour FRR: total FRR wall area = 68.8m2, two single doors $16,900 $18,900 $20,100 $300 $450 $600
123
8.3.4 Type of Transformer
Three types of transformers are evaluated in this research. These include:
Flammable liquid insulated transformer (mineral oil)
Less flammable liquid insulated transformer (silicone oil)
Dry type transformer (dry air)
A mineral oil insulated transformer is chosen as the base transformer type for the assessment.
Through discussion with a senior sales engineer [97], the cost of a mineral oil insulated
transformer is estimated about NZD$26,000 to NZD$28,000. The cost relationship between
other types of transformer and the mineral oil insulated transformer is found in Goudie [56].
Taking the cost of a mineral oil insulated transformer as 100%, the relative initial costs of
silicone oil insulated transformers and dry type transformers are found to be between 125% to
135% and between 130% to 200%, respectively (including the initial cost of the dielectric
fluid). Therefore, the cost of a silicone oil insulated transformer and a dry type transformer are
determined to be in the range of NZD$32,500 to NZD$37,800 and NZD$33,800 to
NZD$56,000, respectively, as shown in Table 8-5.
The Hydroelectric Research and Technical Services Group [119] states that transformer oil
rehabilitation should take place at the 10-year point and so on until the end of the useful
lifetime of the transformer (approximately 30 years). Therefore, it is assumed the entire
volume of transformer oil is replaced once every 10 years. In the recent market, the cost of
mineral oil and silicone oil is found to be NZD$15 to NZD$30 and NZD$12 to NZD$15 per
litre, respectively. Hence, for a transformer containing about 550L to 840L of oil, the cost of
oil retrofill is estimated to be NZD$8,250 to NZD$25,200 (mineral oil) and NZD$6,600 to
NZD$12,600 (silicone oil). Assuming the retrofill cost is equally split into 10 years, the
replacement cost is estimated to be about NZD$825 to NZD$2520 (mineral oil) and
NZD$660 to NZD$1,260 (silicone oil) per year.
For the inspection and testing cost, the senior sales engineer [97] suggested that the annual
maintenance cost of liquid type transformers is to be at least twice that of the dry type
transformers. Note that the maintenance cost relationship between liquid type and dry type
124
transformers recommended is in disagreement with the reference by Goudie and Chatterton
[56] as indicated in Section 4.7.1. It is because the testing cost of the dielectric materials are
excluded in Goudie and Chatterton [56]. Therefore, the maintenance cost relationship
proposed by the senior sales engineer [97] is used in the assessment. As advised, the
maintenance cost of liquid type transformers is about NZD$400 to NZD$600 per year.
Therefore, the maintenance cost of dry type transformers is estimated to be NZD$200 to
NZD$300 per year. Note that replacement costs of a dry type transformer are likely to be low
and is generally included in the inspection and testing costs. Therefore, it is neglected in the
assessment. A summary of the initial costs and annual costs of different types of transformers
are shown in Table 8-6.
Table 8-5: Cost of different types of transformer Description Cost (NZD$)
System/ Installation cost Flammable liquid insulated transformer (mineral oil) $26,000 - $28,000
Inspection and testing cost Expert engineer justified $400 - $600 pa
Replacement cost Replace once in 10 years. Oil costs $15 - $30 per liter with a total of 550L - 840L oil $830 - $2,520 pa
System/ Installation cost
Less flammable liquid insulated transformer (Silicone oil): 25%~35% above the cost of a mineral oil insulated transformer
$32,500 - $37,800
Inspection and testing cost Expert engineer justified $400 - $600 pa
Replacement cost Replace once in 10 years. Oil costs $12 - $15 per liter with a total of 550L - 840L oil $660 - $1,260 pa
System/ Installation cost Dry type transformer (Dry air): 30%~100% above the cost of a mineral oil insulated transformer
$33,800 - $56,000
Inspection and testing cost Expert engineer justified $200 - $300 pa
Replacement cost Very low and is included in the inspection and testing cost Neglect
Table 8-6: Initial costs and annual costs of different types of transformers Initial cost (NZD$) Annual cost (NZD$) Relevant
scenarios Description Min. Mean Max. Min. Mean Max.
Scenario 1 – 10 Liquid type (Mineral oil) $26,000 $27,000 $28,000 $1,230 $1,990 $3,120
Scenario 4a, 7a Liquid type (Silicone oil) $32,500 $35,200 $37,800 $1,060 $1,400 $1,860
Scenario 4b, 7b Dry type (Dry air) $33,800 $44,900 $56,000 $200 $250 $300
125
8.3.5 Summary of the Cost Estimate
A summary of the initial costs and annual costs for each scenario is shown in Table 8-7.
Table 8-7: Summary of initial costs and annual costs (Mean value only) Sprinkler system FRR construction Transformer type Total cost
IC (NZD$)
Ac (NZD$)
IC (NZD$)
Ac (NZD$)
IC (NZD$)
Ac (NZD$)
IC (NZD$)
Ac (NZD$)
Scenario 1 (Base case 1) $0 $0 $12,330 $450 $27,000 $1,990 $39,330 $2,440
Scenario 2 $0 $0 $13,140 $450 $27,000 $1,990 $40,140 $2,440Scenario 3 $0 $0 $15,440 $450 $27,000 $1,990 $42,440 $2,440Scenario 4 $0 $0 $15,980 $450 $27,000 $1,990 $42,980 $2,440Scenario 5 $0 $0 $18,640 $450 $27,000 $1,990 $45,640 $2,440Scenario 6 $12,000 $800 $12,330 $450 $27,000 $1,990 $51,330 $3,240Scenario 7 $12,000 $800 $13,140 $450 $27,000 $1,990 $52,140 $3,240Scenario 8 $12,000 $800 $15,440 $450 $27,000 $1,990 $54,440 $3,240Scenario 9 $12,000 $800 $15,980 $450 $27,000 $1,990 $54,980 $3,240Scenario 10 $12,000 $800 $18,640 $450 $27,000 $1,990 $57,640 $3,240
Scenario 4 (Base case 2)
$0 $0 $15,980 $450 $27,000 $1,990 $42,980 $2,440
Scenario 4a $0 $0 $15,980 $450 $35,100 $1,390 $51,080 $1,840Scenario 4b $0 $0 $15,980 $450 $44,550 $250 $60,530 $700
Scenario 7 (Base case 3)
$12,000 $800 $13,140 $450 $27,000 $1,990 $52,140 $3,240
Scenario 7a $12,000 $800 $13,140 $450 $35,100 $1,390 $60,240 $2,640Scenario 7b $11,000 $800 $13,140 $450 $44,550 $250 $68,690 $1,500
Note: Ic is the initial costs and Ac is the annual costs
126
8.4 Risk Reduction Benefit Cost Ratio
According to Barry [93], Cost Benefit ratio (B/C) can be determined using Equation 8-1.
Given the present worth factor (P/A, i, N) of 12.41, the equation of benefit cost ratio can be
rewritten by substituting Equation 8-2 and Equation 8-3, as follows:
Equation 8-5: ( )
C
Cme
IARRCB −−⋅
=41.12/
Based on the estimated total risk in Section 7.8 and the initial and annual costs in Section
8.3.5, the B/C ratio for the risk reduction strategies are determined using Equation 8-5. Note
that the estimated total risk of the base case is considered as the existing risk (Re) while the
estimated total risk of the alternatives is the modified risk (Rm). In the B/C ratio calculation,
the initial costs (IC) and annual costs (AC) of the alternatives are determined based on the cost
difference from its respective base case.
For scenarios being a base case, no B/C ratio is expected since no risk benefit is expected. A
summary of the results of the B/C ratio calculation is indicated in Table 8-8 (Also refer to
Appendix F). In addition, the ranking of the B/C ratio of the alternatives are listed
systematically in Table 8-9 through Table 8-11.
127
Table 8-8: A summary of the results of the B/C ratio calculation
1 Existing risk, Re (NZD$)
1 Modified risk, Rm (NZD$)
2 Risk benefit RB (NZD$)
3 Initial costs IC (NZD$)
3 Annual costs AC (NZD$)
B/C ratio
Scenario 1 (Base case 1)
49,690 $0 N/A
Scenario 2 49,690 $0 $810 $0 0.0
Scenario 3 49,330 $360 $3,110 $0 1.4
Scenario 4 48,620 $1,080 $3,650 $0 3.7
Scenario 5 47,990 $1,700 $6,310 $0 3.4
Scenario 6 32,520 $17,180 $12,000 $850 16.9
Scenario 7 32,520 $17,180 $12,810 $850 15.8
Scenario 8 32,490 $17,210 $15,110 $850 13.4
Scenario 9 32,420 $17,270 $15,650 $850 13.0
Scenario 10 32,370 $17,320 $18,310 $850 11.2
Scenario 4 (Base case 2)
48,620 $0 $0 $0 N/A
Scenario 4a 47,960 $650 $8,100 ($560) 1.9
Scenario 4b 47,900 $720 $17,550 ($1,740) 1.7
Scenario 7 (Base case 3)
32,520 $0 $0 $0 N/A
Scenario 7a 32,470 $50 $8,100 ($600) 1.0
Scenario 7b 32,360 $150 $16,550 ($1,740) 1.4
1 Note that the estimated total risk of the base case is the existing risk, Re, and the estimated total
risk of the alternatives is the modified risk, Rm. 2 Risk benefit is the difference between the existing risk, Re and the modified risk, Rm. 3 Initial costs, IC, and annual costs, AC, in the table indicate the cost difference from its respective
base case; hence, when the required costs of alternatives are less then the costs of its respective
base case, negative costs may result (as shown in the brackets).
* N/A – Not applicable
128
Table 8-9: Ranking of the B/C ratios with Scenario 1 as the base case
Rank B/C ratio Scenario
Smoke detection system
Sprinkler system
FRR construction Transformer type
----- N/A Scenario 1 Yes No 30 minute Mineral oil insulated transformer
1 16.9 Scenario 6 Yes Yes 30 minute Mineral oil insulated transformer
2 15.8 Scenario 7 Yes Yes 1 hour Mineral oil insulated transformer
3 13.4 Scenario 8 Yes Yes 2 hour Mineral oil insulated transformer
4 13.0 Scenario 9 Yes Yes 3 hour Mineral oil insulated transformer
5 11.2 Scenario 10 Yes Yes 4 hour Mineral oil insulated transformer
6 3.7 Scenario 4 Yes No 3 hour Mineral oil insulated transformer
7 3.4 Scenario 5 Yes No 4 hour Mineral oil insulated transformer
8 1.4 Scenario 3 Yes No 2 hour Mineral oil insulated transformer
9 0.0 Scenario 2 Yes No 1 hour Mineral oil insulated transformer * N/A – Not applicable
Table 8-10: Ranking of the B/C ratios with Scenario 4 as the base case
Rank B/C ratio Scenario
Smoke detection system
Sprinkler system
FRR construction Transformer type
----- N/A Scenario 4 Yes No 3 hour Mineral oil insulated transformer
1 1.9 Scenario 4a Yes No 3 hour Silicone oil insulated transformer
2 1.7 Scenario 4b Yes No 3 hour Dry type transformer * N/A – Not applicable
Table 8-11: Ranking of the B/C ratios with Scenario 7 as the base case
Rank B/C ratio Scenario
Smoke detection system
Sprinkler system
FRR construction Transformer type
----- N/A Scenario 7 Yes Yes 1 hour Mineral oil insulated transformer
1 1.0 Scenario 7b Yes Yes 1 hour Dry type transformer
2 1.4 Scenario 7a Yes Yes 1 hour Silicone oil insulated transformer * N/A – Not applicable
129
8.5 Discussion
Overall, it is found that scenarios with a sprinkler system, such as Scenario 6 to Scenario 10,
would generally have higher C/B ratio than scenarios with no sprinkler protection, such as
Scenario 1 to Scenario 5. As the results of the B/C analysis, Scenario 6 is found to be the
economically best option and followed by scenarios having a higher FRR construction.
In scenarios with sprinkler protection, it is found that the higher FRR construction would have
the lower the B/C ratio, (The B/C ratio is reduced from 16.9 for Scenario 6 (FRR of 30
minutes) to 11.2 for Scenario 10 (FRR of 4 hours). In scenarios without sprinkler protection,
the scenario with a 3 hour FRR construction (Scenario 4) is considered to be the most cost-
effective solution in terms of occupants’ life safety consequence.
In general, the results of the assessment agree with most of the regulation standards and the
non-regulation guidelines as studied in the literature review section. The fire safety design
options required by the standards and guidelines in Section 1.1 with respect to the
corresponding B/C ratio determined are indicated in Table 8-12.
Table 8-12: The ranking for the fire safety design options required in the standards and guidelines
Option C/AS 1 NZFS NFPA BCA IEEE FM Global
Electricity provider (1)
Electricity provider (2)
1 9th 7th 6th N/A N/A 6th 8th 8th
2 N/A N/A. 2nd 3rd N/A. 2nd N/A 2nd
* N/A = Not applicable
It should be noted that the analysis consists of a certain amount of uncertainty, such as the
cost of sprinkler systems and inspections are evaluated based only on engineering judgement.
These costs may be different from one case to another.
As known, a B/C ratio of greater than one implies the scenario is a beneficial investment
whilst a B/C ratio less than one implies it is a loss investment. In this case, the B/C ratio for
all scenarios is well above the critical value of one. This result not only shows that all
alternative scenarios are beneficial investments, it also indicates that the alternative scenarios
130
are very cost-effective. The total risk for the first ten scenarios and their corresponding B/C
ratio are shown in Figure 8-2.
$0
$10,000
$20,000
$30,000
$40,000
$50,000
$60,000
1 2 3 4 5 6 7 8 9 10
Scenario
Estim
ated
tota
l ris
k (N
ZD$/
inci
dent
)
0
2
4
6
8
10
12
14
16
18
B/C
ratio
Estimated total risk B/C ratio
Figure 8-2: Estimated total risk of the alternatives and their corresponding B/C ratio
As can be seen, the total risk for the scenarios containing sprinkler systems, i.e. Scenario 6 to
Scenario 10, is relatively low (The EMV is about NZD$30,000) compared to the scenarios
without sprinkler systems, Scenario 1 to Scenario 5 (The EMV is about NZD$50,000). It
should be noted that in the case of a sprinklered building, where the cost of extending the
sprinkler system to the distribution substation is considered to be low compared to a non-
sprinklered building. It may result a higher B/C ratio for scenarios with sprinkler system due
to the reduced cost. Further study may be required to carry on the comparison between the
buildings with and without sprinkler protection.
In the event of mineral oil insulated transformer fire in a distribution substation, large
amounts of fuel is expected in the room due to the presence of oil. In such cases, if sprinkler
systems are not installed, such as Scenario 1 to Scenario 5, low FRR construction is not
considered to be sufficient to confine the fire. This concept is in agreement with the results of
131
the B/C analysis, where Scenario 2 (1 hour FRR and no sprinkler system) and Scenario 3
(2 hour FRR and no sprinkler system) are both ranked near the bottom among the 9
alternatives. On the other hand, if sprinkler systems are installed, such as Scenario 6 to
Scenario 10, according to the results of the B/C analysis, a construction having a FRR of 30
minute (Scenario 6) is considered to be the most cost-effective solution.
In the second part of the B/C analysis, two other types of transformers replacing the
flammable liquid (mineral oil) insulated transformer in a distribution substation are assessed.
These are the less flammable liquid insulated (silicone oil) transformer and the dry type (dry
air) transformer. As the results of the B/C analysis indicate, both these transformers are
considered as a beneficial investment. This meant that replacing an existing mineral oil
insulated transformer with a silicone oil or dry air insulated transformer is considered to be
cost effective based on the B/C analysis presented in this report.
It was found that the B/C ratio of less flammable liquid insulated transformers can be higher
or lower than the B/C ratio of the dry type transformers depending on the existing fire safety
design of the distribution substation. In the case of Scenario 4, as the base case, the scenario
with the less flammable liquid insulated transformer has a higher B/C ratio. This result is
considered to be reasonable since the dry type transformers are known as low hazard
equipment and, thus, 3 hour FRR construction seems to be redundant. On the other hand, in
the case of Scenario 7, as the base case, the scenario with the dry type transformer has a
higher B/C ratio.
Overall, it is found that using sprinkler system or replacing transformers with lower hazard in
distribution substation can sufficiently reduce the fire risk to occupants in a high-rise building.
132
CHAPTER 9 CONCLUSIONS AND RECOMMENDATIONS
The following conclusions can be drawn from this analysis:
Fire safety design requirements for distribution substations are obtained from
different standards and guidelines. However, the requirements in these documents are
inconsistent. For a distribution substation containing a flammable liquid insulated
transformer with no sprinkler system installed, the recommended fire separation
constructions vary between 1 hour FRR and 4 hour FRR. When sprinkler systems are
installed, the fire separation can generally reduce to 2 hour FRR or lower. Moreover,
only one standard and one guideline provided the fire safety design of distribution
substation containing less flammable liquid insulated transformers. As recommended,
fire separation construction having a FRR of 1 hour or 3 hour is required in a non-
sprinklered distribution substation. When sprinkler systems are installed, no FRR
constructions are required. Typically, a dry type transformer does not carry any a
high hazard materials, hence, no fire separation constructions are required.
According to data provided by the NZFS FIRS [65], there were a total of 20 structure
fires originating in distribution substations, in typical New Zealand buildings, during
the 6 year period from January 2000 to January 2006. There were 13 fire incidents
involving faults in the electrical wire and wiring insulation, and 4 fire incident having
transformer and transformer fluid as the object first ignited. No fatalities were
recorded for these fire incidents. In addition, it is found that the total number of
distribution substations in New Zealand increased from about 24,000 in 1946 to
about 170,000 in 2006.
The number of structure fires originating in switchgear areas or transformer vaults
(distribution substation) and their consequences are obtained from the NFIRS.
During the 22 year period from 1980 to 2002, an average of 1251 fires, 71 civilian
injuries and 3 civilian deaths were recorded each year.
133
The reliability of transformers and fire protection systems were studied in this
research. Typical failure rates for transformers (fires may or may not occur) are
found to be in the range of 0.2 x 10-3 to 140 x 10-3 failures per year. The reliability of
smoke detection systems and sprinkler systems for general buildings were found to
be in the range of 77.8% to 94% and 81.3% to 99.5%, respectively.
The statistical data used in this research may contain uncertainties due to the lack of
information on the specified data for the fire safety protection systems, such as the
reliability of smoke detection systems and sprinkler systems in distribution substation.
Hence, further studies may be required for obtaining a more accurate result.
As a result of the Event Tree Analysis, the overall risks are obtained for a total of 14
scenarios. The probability of the various consequences is calculated by multiplying
the various branch probabilities of each factor and the consequences are determined
based on the rates of civilian causalities in a fire and the value of statistical life
(VSL). From literature, the value of statistical life is found to be $3 million for a
death and $250,000 for an injury. As the result of the ETA analysis, Scenario 1,
which contains the lowest level of fire safety design compared to the other scenarios,
has the highest total risk, NZD$49,690 per transformer fire incident in a substation.
As the level of fire safety increases, the total risk is expected to be reduced. Using the
same type of transformer (Scenario 1 to Scenario 10), Scenario 10, which contains
the highest level of fire safety design compared to the other scenarios, has reduced
the total risk to NZD$32,370 per transformer fire incident in a substation.
From the Cost-Benefit Analysis, it is found that construction having a FRR of 4 hour
and no sprinkler system installed, as proposed by the NZFS, is not considered to be
the economically best option. As the result of the C/B ratio ranking, it is found that
scenarios with a sprinkler system (Scenario 6 to Scenario 10) would generally have
more cost benefit than scenarios without sprinkler system (Scenario 2 to scenario 5).
Out of the nine scenarios having the same transformer type, Scenario 6 (sprinkler
system provided/ 30 minutes FRR construction) is found to be the most cost effective
scenario with a B/C ratio of 16.9. Moreover, in a non- sprinklered building, a
scenario with 3 hours FRR construction (Scenario 4) is found to have the highest B/C
134
ratio (3.7). Note that the cost-benefit analysis in this research does not concern the
property damage, business continuity or environment damage caused by transformer
fires or fire extinguishments.
As a result of this study, the following recommendations are offered:
The proposed four hour fire separation between the distribution substations and the
interior spaces of the building, when no sprinkler system is provided, is not
considered to be the most cost-effective alternative to the life safety of the building
occupants.
From the life safety perspective, distribution substation in a high rise building is
recommended to be protected by sprinklers and smoke detectors. If sprinkler system
is provided, the FRR construction of the substation could be reduced to 30 minutes.
If sprinkler system is not provided, construction may be required to have a higher
FRR. As the result of the analysis, 3 hour FRR construction is determined to have the
highest cost-benefit ratio in a non-sprinklered building.
In addition, replacing a flammable liquid insulated transformer with a less flammable
liquid insulated transformer or a dry type transformer is generally considered to be
economical alternatives.
Future research is recommended in the following areas:
The 20 fire incidents in distribution substations, used in the report are not considered
to be sufficient and representative. Further statistical analysis of indoor transformer
fire incidents is recommended in order to obtain a more accurate result.
Conduct more detailed modeling to predict the environment conditions, the effect of
toxic substances and effect of fires and explosions on building occupants.
Explosion hazards are one of the main concerns in the event of a transformer fire.
Further studies may be required in this particular area.
135
In addition to the occupant life safety as evaluated in this research, Clauses C1 – C4
of the NZBC also requires the prevention of fire spread to adjacent properties and the
protection of fire service personnel during fire rescue operations. To provide a
complete assessment and recommendations on the fire protection for indoor
distribution substation in residential buildings, further studies on these aspects is
needed.
136
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144
APPENDIX A: Transformer and Associated Equipment Appendix A1 - Site Visit (1): Christchurch city centre
Figure A1.1: 750kVA mineral oil fluid transformer
Figure A1.2: Circuit board
145
Figure A1.3: Cables terminal
146
Figure A1.4: High voltage switchgear
147
Figure A1.5: Low voltage switchgear
Figure A1.6: Cable tray
148
Appendix A2 - Site visit (2): University of Canterbury
Figure A2.1: 750kVA mineral oil fluid transformer on an oil containment
Conservator or Expansion tank
Pressure monitor meter
Tap changer
149
Figure A2.2: Oil insulated high voltage switchgear
Figure A2.3: Low voltage switchgear
150
Figure A2.4: Wall opening in a distribution station
Figure A2.5: Combustible material (wooden board) in a distribution substation
151
APPENDIX B: Distribution Substation Fire Safety Protection Required by the NZFS
1) Place transformers and switchgear in separate rooms within vaults (distribution
substation). A fire resistance rating of not less than F60 (1 hour rating) should apply
to these partitions and all openings and penetrations in them.
2) Separate vaults (distribution substation) from the interior spaces of buildings by walls
and floor/ceiling assemblies having fire resistance ratings not less than F240 (4-hour
rating) with suitable fire resistance rated protection of all openings and penetrations.
3) Provide direct exterior access to transformer vaults (distribution substation) by means
of a full-sized door (minimum clear opening area of 800 x 2100mm) wherever possible.
4) Cable penetrations in fire resistance rated walls separating other interior spaces of
the building from the vaults (distribution substation) should occur within 1.0m of the
floor to avoid placing openings near ceilings where smoke, flames and heated gases
may accumulate and spread in a fire situation.
5) No penetrations should be permitted in the floor/ceiling assemblies separating a vault
(distribution substation) from upper floors, and if at all possible installations in
basements should be avoided altogether.
6) Cable feeds into equipment should be from the top rather than the bottom to avoid
placing cables in an area where burning transformer oil or fire suppression water
may pool.
7) Transformers and switchgear should be installed on plinths or platforms above the
floor level to prevent connections inside equipment cabinets from coming into contact
with burning transformer oil or fire suppression water.
152
8) Bunding of sufficient capacity to contain the contents of the largest transformer and a
quantity of fire suppression water equal to that expected for 20 minutes flow from
manual or automatic appliances should be provided.
9) Install a sump pit and suction connection to provide for the removal of oil and water
from the room without the need for entry.
10) In building protected by automatic sprinkler systems, provide automatic sprinkler
protection for transformer rooms within vaults (distribution substation). Provide gas
flood or water mist systems in switchgear room.
11) Provide deflagration venting direct to the building exterior from transformer rooms
within vaults (distribution substation) or design the room to withstand and contain the
pressure developed from a transformer explosion within the space.
12) In buildings without automatic fire sprinkler systems, no additional fire protection
need be installed beyond that required by the New Zealand Building Code.
Nevertheless, we strongly encourage “the company” to install automatic heat
detection in these and subscribe to appropriate monitoring and notification services to
obtain early warning of a fire that may affect the reliability of the distribution grid.
New Zealand fire Service - Whakaratonga Iwi
Christchurch,
New Zealand
153
APPENDIX C: Statistical data of Transformer Fires in Distribution Substations
The table below shows the statistical data for the number of distribution substations in New
Zealand between 1946 and 1995 and the estimated number of distribution substations between
1996 and 2006. Refer to the New Zealand Energy and Resources Division and Market
Information and Analysis Group [70], the New Zealand Energy Modelling and Statistics Unit
[71] and [72], and the New Zealand Ministry of Energy [73]
Year ending 31st March Number of substations Year ending 31st March Number of
substations 1946 23559 1977 97961 1947 24361 1978 101010 1948 25271 1979 103586 1949 26395 1980 106056 1950 27795 1981 108581 1951 28880 1982 111135 1952 30350 1983 113548 1953 31931 1984 116212 1954 33787 1985 119159 1955 36112 1986 121954 1956 38277 1987 124864 1957 40415 1988 119008 1958 42643 1989 127262 1959 44702 1990 128918 1960 46911 1991 130948 1961 49312 1992 134205 1962 51838 1993 133692 1963 54377 1994 135656 1964 56645 1995 138695 1965 58200 1996 141330 1966 62318 1997 144015 1967 65624 1998 146752 1968 68687 1999 149540 1969 71300 2000 152381 1970 74847 2001 155277 1971 78143 2002 158227 1972 81677 2003 161233 1973 84647 2004 164297 1974 87839 2005 167418 1975 90925 2006 170599 1976 94671
154
The following tables show the data on distribution substation fire incidents recorded by the
NZFS FIRS between 2000 and 2006 [65].
Number of fires
Year Number of fires January 2000 - January 2001 4 January 2001 - January 2002 0 January 2002 - January 2003 5 January 2003 - January 2004 4 January 2004 - January 2005 3 January 2005 - January 2006 4
Monthly trends
Month Number of fires January 3 February 1 March 1 April 0 May 1 June 4 July 3 August 2 September 1 October 1 November 1 December 2
Time of day
Time period of day Number of fires 23:00 ~ 03:00 3 03:00 ~ 07:00 3 07:00 ~ 11:00 5 11:00 ~ 15:00 4 15:00 ~ 19:00 2 19:00 ~ 23:00 3
155
Supposed Causes
Supposed causes Number of fires Electrical failure 12 60.0% Lack of maintenance 1 5.0% Equipment overloaded (includes electric cords serving too many appliances) 4 20.0%
Mechanical failure or malfunction 2 10.0% Unknown 1 5.0%
Primary ignition object
Item First Ignited Number of fires Electrical wire, Wiring insulation 13 65.0% Transformer, Transformer fluids 4 20.0% Other known item first ignited 3 15.0%
Equipment involved 1 Equipment involved Number of fires
Transformer & associated equipment - Circuit breakers associated with transformers 4 20.0%
Transformer & associated equipment - Distribution type 7 35.0%
Transformers & associated equipment - not classified above 1 5.0%
Information not recorded 6 30.0% Other known equipment: Power cable, controlling switch 2 10.0%
1 This provides a classification for the equipment that provided the heat that started the fire, or was
involved in the release of hazardous substances; the equipment involved in the incident is to be listed
when it is identified as providing the heat that started fire or was the cause of the incident;
156
Source of ignition (Heating source) 1 Heat source Number of fires
Short circuit arc 12 60.0% Arc from fault, loose or broken conductor 2 10.0% Heat from overloaded equipment 2 10.0% Other known heat source 4 20.0%
1 This provides a classification for the form of heat energy igniting the fire e.g. flame, spark or hot
surface
Extent flame damage
Extent of flame damage Number of fires No damage of this type 0 Confined to object of origin 5 Confined to room of origin 1 Confined to structure of origin 6 Unknown 8
Extent smoke damage
Extent of smoke damage Number of fires No damage of this type 3 Confined to object of origin 1 Confined to part of room or area of origin 1 Confined to room of origin 2 Confined to structure of origin 5 Unknown 8
157
The table below shows the statistical data on the consequence of transformer fire incidents
recorded in the NFIRS between 1980 and 2002 [66].
Direct Property Damage (Million) Year Number of
transformer fires Number of
Deaths Number of
injuries (million NZ$) (x1000 NZD$/ fire)
1980 1890 15 48 52.0 27.5 1981 1730 5 91 52.3 30.2 1982 1770 0 50 54.2 30.6 1983 1580 0 95 45.1 28.6 1984 1650 0 174 49.3 29.9 1985 1650 2 84 37.3 22.6 1986 1520 8 94 46.5 30.6 1987 1480 2 91 59.8 40.4 1988 1280 4 69 67.5 52.7 1989 1310 2 77 49.7 38.0 1990 1240 5 72 45.9 37.0 1991 1100 0 57 53.6 48.7 1992 1260 0 121 55.5 44.1 1993 1090 0 103 76.2 69.9 1994 1180 1 85 31.5 26.7 1995 1000 0 93 55.5 55.5 1996 1000 0 35 42.5 42.5 1997 990 6 26 45.3 45.7 1998 1030 3 28 67.2 65.2 1999 880 6 41 20.0 22.8 2000 730 0 55 27.7 37.9 2001 730 2 31 69.8 95.6 2002 680 0 18 56.0 82.4
Average 1250.9 2.7 71.2 50.5 40.3
158
APPENDIX D: Calculation of the Probability of Manual Fire Fighting Performance
The probability that the Fire Service can control fires is found in Fontana et al. [100]. As
stated, the probability that fire spread is stopped by fire firefighters for general buildings is in
the range of 0.8 to 0.95. Since the research only provides details on the PMFF for commercial
buildings, the ratio between the PMFF in different situation for commercial buildings is used to
determine the PMFF for general buildings. The calculations are shown in Table D-1.
1 Commercial building
Firefighters' ability Early warning alarm PMFF_S
(ta_a < 10 minutes)Ratio
PMFF_S (ta_a > 10 minutes)
Ratio
Professional Not provided 0.95 0.95/0.95 = 100%
0.85 0.85/0.95 = 89.5%
Professional Provided 0.988 0.988/0.95
= 104% 0.963
0.963/0.95 = 101.4%
1 The performance of PMFF is given for commercial building. Use it as a base and determined the ratio.
General building Upper bound (PMFF = 0.95 where professional firefighter and no early warning alarm provided)
Firefighters' ability Early warning alarm PMFF_S (ta_a < 10 minutes) PMFF_S (ta_a > 10 minutes) Professional Not provided 0.95 * 100% = 0.95 0.95 * 89.5% = 0.85 Professional Provided 0.95 * 104% = 0.988 0.95 * 101.4% = 0.963
General building Lower bound (PMFF = 0.80 where professional firefighter and no early warning alarm provided)
Firefighters' ability Early warning alarm PMFF_S (ta_a < 10 minutes) PMFF_S (ta_a > 10 minutes) Professional Not provided 0.80 * 100% = 0.80 0.80 * 89.5% = 0.761 Professional Provided 0.80 * 104% = 0.832 0.80 * 101.4% = 0.811
Same approach is used to determine the probability of the non-professional firefighter
controlling the fire. The overall results are shown in Table D-2 as follow:
General building
Firefighters' ability Early warning alarm PMFF_S
(ta_a <10 min) PMFF_S
(ta_a >10 minutes) Professional firefighters Not provided 80.0% - 95.0% 71.6% - 85.0% Non-professional firefighters Not provided 75.8% - 90.0% 67.4% - 80.0% Professional firefighters Provide 83.2% - 98.8% 81.1% - 96.3% Non-professional firefighters Provide 82.1% - 97.5% 71.6% - 85.0%
159
APPENDIX E: Probability Distribution of the Total Risk for each scenario
Scenario 1: No sprinkler system, 30 minute FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.800 1.000 0.27602 47750 13180 3 0.855 1.000 0.403 0.200 0.000 0.00000 47750 0 4 0.855 1.000 0.403 0.200 1.000 0.06900 55300 3816 5 0.855 1.000 0.597 0.777 1.000 0.39659 47750 18937 6 0.855 1.000 0.597 0.223 0.000 0.00000 47750 0 7 0.855 1.000 0.597 0.223 1.000 0.11382 55300 6294 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.765 1.000 0.04461 48775 2176
10 0.145 1.000 0.403 0.235 0.000 0.00000 48775 0 11 0.145 1.000 0.403 0.235 1.000 0.01370 58650 804 12 0.145 1.000 0.597 0.673 1.000 0.05805 48775 2831 13 0.145 1.000 0.597 0.327 0.000 0.00000 48775 0 14 0.145 1.000 0.597 0.327 1.000 0.02821 58650 1654
Total: 1.00000 Total: 49692 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 49,013 5% $ 49,311
Maximum $ 50,446 50% $ 49,376
Mean $ 49,693 95% $ 49,436
Std Dev $ 235
Distribution for Scenario 1 F ire riskE M V /D196
Val
ues
in 1
0 -
3
V alues in Thousands
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
M ean=49693.32
49 49.4 49.8 50.2 50.6
@ RISK Student V ersionFor A cademic U se Only
49 49.4 49.8 50.2 50.6
5% 90% 5% 49.311 50.08
M ean=49693.32
160
Scenario 2: No sprinkler system, 1 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.800 1.000 0.27602 47750 13180 3 0.855 1.000 0.403 0.200 0.000 0.00000 47750 0 4 0.855 1.000 0.403 0.200 1.000 0.06900 55300 3816 5 0.855 1.000 0.597 0.777 1.000 0.39659 47750 18937 6 0.855 1.000 0.597 0.223 0.000 0.00000 47750 0 7 0.855 1.000 0.597 0.223 1.000 0.11382 55300 6294 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.765 1.000 0.04461 48775 2176
10 0.145 1.000 0.403 0.235 0.000 0.00000 48775 0 11 0.145 1.000 0.403 0.235 1.000 0.01370 58650 804 12 0.145 1.000 0.597 0.673 1.000 0.05805 48775 2831 13 0.145 1.000 0.597 0.327 0.000 0.00000 48775 0 14 0.145 1.000 0.597 0.327 1.000 0.02821 58650 1654
Total: 1.00000 Total: 49692 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 49,013 5% $ 49,311
Maximum $ 50,446 50% $ 49,376
Mean $ 49,693 95% $ 49,436
Std Dev $ 235
Distribution for Scenario 2 F ire riskE M V /D197
Val
ues
in 1
0 -
3
V alues in Thousands
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
M ean=49693.32
49 49.4 49.8 50.2 50.6
@ RISK Student V ersionFor A cademic U se Only
49 49.4 49.8 50.2 50.6
5% 90% 5% 49.311 50.08
M ean=49693.32
161
Scenario 3: No sprinkler system, 2 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.800 1.000 0.27602 47750 13180 3 0.855 1.000 0.403 0.200 0.200 0.01380 47750 659 4 0.855 1.000 0.403 0.200 0.800 0.05520 55300 3053 5 0.855 1.000 0.597 0.777 1.000 0.39659 47750 18937 6 0.855 1.000 0.597 0.223 0.200 0.02276 47750 1087 7 0.855 1.000 0.597 0.223 0.800 0.09106 55300 5035 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.765 1.000 0.04461 48775 2176
10 0.145 1.000 0.403 0.235 0.200 0.00274 48775 134 11 0.145 1.000 0.403 0.235 0.800 0.01096 58650 643 12 0.145 1.000 0.597 0.673 1.000 0.05805 48775 2831 13 0.145 1.000 0.597 0.327 0.200 0.00564 48775 275 14 0.145 1.000 0.597 0.327 0.800 0.02257 58650 1323
Total: 1.00000 Total: 49334 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 48,779 5% $ 49,025
Maximum $ 49,949 50% $ 49,079
Mean $ 49,334 95% $ 49,126
Std Dev $ 190
D istribution for Scenario 3 F ire riskE M V /D198
Val
ues
in 1
0 -
3
V alues in Thousands
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
2.000
M ean=49334.29
48.6 48.95 49.3 49.65 50
@ RISK Student V ersionFor A cademic U se Only
48.6 48.95 49.3 49.65 50
5% 90% 5% 49.0246 49.6468
M ean=49334.29
162
Scenario 4: No sprinkler system, 3 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.800 1.000 0.27602 47750 13180 3 0.855 1.000 0.403 0.200 0.600 0.04140 47750 1977 4 0.855 1.000 0.403 0.200 0.400 0.02760 55300 1526 5 0.855 1.000 0.597 0.777 1.000 0.39659 47750 18937 6 0.855 1.000 0.597 0.223 0.600 0.06829 47750 3261 7 0.855 1.000 0.597 0.223 0.400 0.04553 55300 25188 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.765 1.000 0.04461 48775 2176
10 0.145 1.000 0.403 0.235 0.600 0.00822 48775 401 11 0.145 1.000 0.403 0.235 0.400 0.00548 58650 321 12 0.145 1.000 0.597 0.673 1.000 0.05805 48775 2831 13 0.145 1.000 0.597 0.327 0.600 0.01692 48775 825 14 0.145 1.000 0.597 0.327 0.400 0.01128 58650 662
Total: 1.00000 Total: 48616 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 48,311 5% $ 48,449
Maximum $ 48,955 50% $ 48,482
Mean $ 48,616 95% $ 48,506
Std Dev $ 102
Distribution for Scenario 4 F ire riskE M V /D199
Val
ues
in 1
0 -
3
V alues in Thousands
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
M ean=48616.23
48.3 48.475 48.65 48.825 49
@ RISK Student V ersionFor A cademic U se Only
48.3 48.475 48.65 48.825 49
5% 90% 5% 48.4487 48.7851
M ean=48616.23
163
Scenario 5: No sprinkler system, 4 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.800 1.000 0.27602 47750 13180 3 0.855 1.000 0.403 0.200 0.950 0.06555 47750 3130 4 0.855 1.000 0.403 0.200 0.050 0.00345 55300 191 5 0.855 1.000 0.597 0.777 1.000 0.39659 47750 18937 6 0.855 1.000 0.597 0.223 0.950 0.10813 47750 5163 7 0.855 1.000 0.597 0.223 0.050 0.00569 55300 315 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.765 1.000 0.04461 48775 2176
10 0.145 1.000 0.403 0.235 0.950 0.01302 48775 635 11 0.145 1.000 0.403 0.235 0.050 0.00069 58650 40 12 0.145 1.000 0.597 0.673 1.000 0.05805 48775 2831 13 0.145 1.000 0.597 0.327 0.950 0.02680 48775 1307 14 0.145 1.000 0.597 0.327 0.050 0.00141 58650 83
Total: 1.00000 Total: 47988 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 47,886 5% $ 47,924
Maximum $ 48,086 50% $ 47,937
Mean $ 47,988 95% $ 47,946
Std Dev $ 37
D istribution for Scenario 5 F ire riskE M V /D200
V alues in Thousands
0.000
0.002
0.004
0.007
0.009
0.011
0.013
0.016
0.018
0.020
M ean=47987.94
47.85 47.9 47.95 48 48.05 48.1
@ RISK Student V ersionFor A cademic U se Only
47.85 47.9 47.95 48 48.05 48.1
5% 90% 5% 47.924 48.0481
M ean=47987.94
164
Scenario 6: Sprinkler system, 30 minute FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.800 1.000 0.02375 47750 1134 3 0.855 0.086 0.403 0.200 0.000 0.00000 47750 0 4 0.855 0.086 0.403 0.200 1.000 0.00594 55300 328 5 0.855 0.086 0.597 0.777 1.000 0.03412 47750 1629 6 0.855 0.086 0.597 0.223 0.000 0.00000 47750 0 7 0.855 0.086 0.597 0.223 1.000 0.00979 55300 542 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.765 1.000 0.00384 48775 187
10 0.145 0.086 0.403 0.235 0.000 0.00000 48775 0 11 0.145 0.086 0.403 0.235 1.000 0.00118 58650 69 12 0.145 0.086 0.597 0.673 1.000 0.00499 48775 244 13 0.145 0.086 0.597 0.327 0.000 0.00000 48775 0 14 0.145 0.086 0.597 0.327 1.000 0.00243 58650 142
Total: 1.00000 Total: 32516 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,988 5% $ 31,438
Maximum $ 34,459 50% $ 31,621
Mean $ 32,516 95% $ 31,759
Std Dev $ 711
D istribution for Scenario 6 F ire riskE M V /D202
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
M ean=32515.7
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.4384 33.7954
M ean=32515.7
165
Scenario 7: Sprinkler system, 1 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.800 1.000 0.02375 47750 1134 3 0.855 0.086 0.403 0.200 0.000 0.00000 47750 0 4 0.855 0.086 0.403 0.200 1.000 0.00594 55300 328 5 0.855 0.086 0.597 0.777 1.000 0.03412 47750 1629 6 0.855 0.086 0.597 0.223 0.000 0.00000 47750 0 7 0.855 0.086 0.597 0.223 1.000 0.00979 55300 542 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.765 1.000 0.00384 48775 187
10 0.145 0.086 0.403 0.235 0.000 0.00000 48775 0 11 0.145 0.086 0.403 0.235 1.000 0.00118 58650 69 12 0.145 0.086 0.597 0.673 1.000 0.00499 48775 244 13 0.145 0.086 0.597 0.327 0.000 0.00000 48775 0 14 0.145 0.086 0.597 0.327 1.000 0.00243 58650 142
Total: 1.00000 Total: 32516 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,988 5% $ 31,438
Maximum $ 34,459 50% $ 31,621
Mean $ 32,516 95% $ 31,759
Std Dev $ 711
D istribution for Scenario 7 F ire riskE M V /D203
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
M ean=32515.7
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.4384 33.7954
M ean=32515.7
166
Scenario 8: Sprinkler system, 2 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.800 1.000 0.02375 47750 1134 3 0.855 0.086 0.403 0.200 0.200 0.00119 47750 57 4 0.855 0.086 0.403 0.200 0.800 0.00475 55300 263 5 0.855 0.086 0.597 0.777 1.000 0.03412 47750 1629 6 0.855 0.086 0.597 0.223 0.200 0.00196 47750 94 7 0.855 0.086 0.597 0.223 0.800 0.00783 55300 433 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.765 1.000 0.00384 48775 187
10 0.145 0.086 0.403 0.235 0.200 0.00024 48775 11 11 0.145 0.086 0.403 0.235 0.800 0.00094 58650 55 12 0.145 0.086 0.597 0.673 1.000 0.00499 48775 244 13 0.145 0.086 0.597 0.327 0.200 0.00049 48775 24 14 0.145 0.086 0.597 0.327 0.800 0.00194 58650 114
Total: 1.00000 Total: 32485 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,986 5% $ 31,427
Maximum $ 34,376 50% $ 31,607
Mean $ 32,485 95% $ 31,743
Std Dev $ 698
D istribution for Scenario 8 F ire riskE M V /D204
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
M ean=32484.81
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.4271 33.7371
M ean=32484.81
167
Scenario 9: Sprinkler system, 3 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.800 1.000 0.02375 47750 1134 3 0.855 0.086 0.403 0.200 0.600 0.00356 47750 170 4 0.855 0.086 0.403 0.200 0.400 0.00237 55300 131 5 0.855 0.086 0.597 0.777 1.000 0.03412 47750 1629 6 0.855 0.086 0.597 0.223 0.600 0.00588 47750 281 7 0.855 0.086 0.597 0.223 0.400 0.00392 55300 217 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.765 1.000 0.00384 48775 187
10 0.145 0.086 0.403 0.235 0.600 0.00071 48775 34 11 0.145 0.086 0.403 0.235 0.400 0.00047 58650 28 12 0.145 0.086 0.597 0.673 1.000 0.00499 48775 244 13 0.145 0.086 0.597 0.327 0.600 0.00146 48775 71 14 0.145 0.086 0.597 0.327 0.400 0.00097 58650 57
Total: 1.00000 Total: 32423 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,981 5% $ 31,404
Maximum $ 34,209 50% $ 31,580
Mean $ 32,423 95% $ 31,712
Std Dev $ 671
D istribution for Scenario 9 F ire riskE M V /D205
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
M ean=32423.04
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.4041 33.6228
M ean=32423.04
168
Scenario 10: Sprinkler system, 4 hour FRR, Mineral oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.800 1.000 0.02375 47750 1134 3 0.855 0.086 0.403 0.200 0.950 0.00564 47750 269 4 0.855 0.086 0.403 0.200 0.050 0.00030 55300 16 5 0.855 0.086 0.597 0.777 1.000 0.03412 47750 1629 6 0.855 0.086 0.597 0.223 0.950 0.00930 47750 444 7 0.855 0.086 0.597 0.223 0.050 0.00049 55300 27 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.765 1.000 0.00384 48775 187
10 0.145 0.086 0.403 0.235 0.950 0.00112 48775 55 11 0.145 0.086 0.403 0.235 0.050 0.00006 58650 3 12 0.145 0.086 0.597 0.673 1.000 0.00499 48775 244 13 0.145 0.086 0.597 0.327 0.950 0.00231 48775 112 14 0.145 0.086 0.597 0.327 0.050 0.00012 58650 7
Total: 1.00000 Total: 32369 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,977 5% $ 31,386
Maximum $ 34,063 50% $ 31,554
Mean $ 32,369 95% $ 31,682
Std Dev $ 647
Distribution for Scenario 10 F ire riskE M V /D206
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
7
M ean=32368.98
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.3859 33.5253
M ean=32368.98
169
Scenario 4a: No sprinkler system, 3 hour FRR, Silicone oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.865 1.000 0.29845 47750 14251 3 0.855 1.000 0.403 0.135 0.949 0.04418 47750 2110 4 0.855 1.000 0.403 0.135 0.051 0.00239 55300 132 5 0.855 1.000 0.597 0.842 1.000 0.42976 47750 20521 6 0.855 1.000 0.597 0.158 0.949 0.07650 47750 3653 7 0.855 1.000 0.597 0.158 0.051 0.00415 55300 229 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.830 1.000 0.04840 48775 2361
10 0.145 1.000 0.403 0.170 0.949 0.00940 48775 459 11 0.145 1.000 0.403 0.170 0.051 0.00051 58650 30 12 0.145 1.000 0.597 0.738 1.000 0.06366 48775 3105 13 0.145 1.000 0.597 0.262 0.949 0.02144 48775 1046 14 0.145 1.000 0.597 0.262 0.051 0.00116 58650 68
Total: 1.00000 Total: 47964 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 47,852 5% $ 47,899
Maximum $ 48,074 50% $ 47,913
Mean $ 47,964 95% $ 47,923
Std Dev $ 38
D istribution for Scenario 4a F ire riskE M V /D208
Val
ues
in 1
0 -
3
V alues in Thousands
0
1
2
3
4
5
6
7
8
9
10
M ean=47964.02
47.85 47.9 47.95 48 48.05 48.1
@ RISK Student V ersionFor A cademic U se Only
47.85 47.9 47.95 48 48.05 48.1
5% 90% 5% 47.8989 48.0246
M ean=47964.02
170
Scenario 4b: No sprinkler system, 3 hour FRR, Dry type transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.000 ----------- ----------- 1.000 0.00000 31000 0 2 0.855 1.000 0.403 0.910 1.000 0.31397 47750 14992 3 0.855 1.000 0.403 0.090 1.000 0.03105 47750 1483 4 0.855 1.000 0.403 0.090 0.000 0.00000 55300 0 5 0.855 1.000 0.597 0.887 1.000 0.45273 47750 21618 6 0.855 1.000 0.597 0.113 1.000 0.05768 47750 2754 7 0.855 1.000 0.597 0.113 0.000 0.00000 55300 0 8 0.145 0.000 ----------- ----------- 1.000 0.00000 30300 0 9 0.145 1.000 0.403 0.875 1.000 0.05102 48775 2488
10 0.145 1.000 0.403 0.125 1.000 0.00729 48775 355 11 0.145 1.000 0.403 0.125 0.000 0.00000 58650 0 12 0.145 1.000 0.597 0.783 1.000 0.06754 48775 3294 13 0.145 1.000 0.597 0.217 1.000 0.01872 48775 913 14 0.145 1.000 0.597 0.217 0.000 0.00000 58650 0
Total: 1.00000 Total: 47898 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 47,813 5% $ 47,839
Maximum $ 47,976 50% $ 47,851
Mean $ 47,898 95% $ 47,860
Std Dev $ 34
D istribution for Scenario 4b F ire riskE M V /D209
V alues in Thousands
0.000
0.002
0.004
0.007
0.009
0.011
0.013
0.016
0.018
0.020
M ean=47898.18
47.8 47.86 47.92 47.98
@ RISK Student V ersionFor A cademic U se Only
47.8 47.86 47.92 47.98
5% 90% 5% 47.8394 47.9531
M ean=47898.18
171
Scenario 7a: Sprinkler system, 1 hour FRR, Silicone oil insulated transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ transformer fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.865 1.000 0.02568 47750 1226 3 0.855 0.086 0.403 0.135 0.010 0.00004 47750 2 4 0.855 0.086 0.403 0.135 0.990 0.00397 55300 219 5 0.855 0.086 0.597 0.842 1.000 0.03697 47750 1766 6 0.855 0.086 0.597 0.158 0.010 0.00007 47750 3 7 0.855 0.086 0.597 0.158 0.990 0.00687 55300 380 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.830 1.000 0.00416 48775 203
10 0.145 0.086 0.403 0.170 0.010 0.00001 48775 0 11 0.145 0.086 0.403 0.170 0.990 0.00084 58650 50 12 0.145 0.086 0.597 0.738 1.000 0.00548 48775 267 13 0.145 0.086 0.597 0.262 0.010 0.00002 48775 1 14 0.145 0.086 0.597 0.262 0.990 0.00192 58650 113
Total: 1.00000 Total: 32470 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,987 5% $ 31,418
Maximum $ 34,296 50% $ 31,601
Mean $ 32,470 95% $ 31,736
Std Dev $ 691
D istribution for Scenario 7a F ire riskE M V /D211
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
M ean=32470.2
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.4177 33.7028
M ean=32470.2
172
Scenario 7b: Sprinkler system, 1 hour FRR, dry type transformer
Outcome event No. SDS SS FAT MFF WBI
Probability of each
outcome Consequence EMV (NZD$)
Risk NZD$/ fire incident
1 0.855 0.914 ----------- ----------- 1.000 0.78184 31000 24237 2 0.855 0.086 0.403 0.910 1.000 0.02701 47750 1290 3 0.855 0.086 0.403 0.090 1.000 0.00267 47750 128 4 0.855 0.086 0.403 0.090 0.000 0.00000 55300 0 5 0.855 0.086 0.597 0.887 1.000 0.03895 47750 1860 6 0.855 0.086 0.597 0.113 1.000 0.00496 47750 237 7 0.855 0.086 0.597 0.113 0.000 0.00000 55300 0 8 0.145 0.914 ----------- ----------- 1.000 0.13213 30300 4004 9 0.145 0.086 0.403 0.875 1.000 0.00439 48775 214
10 0.145 0.086 0.403 0.125 1.000 0.00063 48775 31 11 0.145 0.086 0.403 0.125 0.000 0.00000 58650 0 12 0.145 0.086 0.597 0.783 1.000 0.00581 48775 283 13 0.145 0.086 0.597 0.217 1.000 0.00161 48775 79 14 0.145 0.086 0.597 0.217 0.000 0.00000 58650 0
Total: 1.00000 Total: 32361 Note that the values above only show the mean values of the distributions.
Simulation result from @Risk4.5
Summary Statistics Statistic Value %tile Value Minimum $ 30,976 5% $ 31,384
Maximum $ 34,042 50% $ 31,550
Mean $ 32,361 95% $ 31,678
Std Dev $ 643
Distribution for Scenario 7b F ire riskE M V /D212
Val
ues
in 1
0 -
4
V alues in Thousands
0
1
2
3
4
5
6
7
M ean=32361.26
30.5 31.5 32.5 33.5 34.5
@ RISK Student V ersionFor A cademic U se Only
30.5 31.5 32.5 33.5 34.5
5% 90% 5% 31.3836 33.5126
M ean=32361.26
173
APPENDIX F: Calculation of the Cost Benefit Ratio
1 Existing risk, Re (NZD$) 1 Modified risk, Rm (NZD$)
2 Risk benefit RB (NZD$)
3 Initial costs IC (NZD$)
3 Annual costs AC (NZD$)
Interest rate, i
Useful life time, N (Year) (P/A,i,n) B/C
ratio Rank
Scenario 1 (Base case 1) $49,692 $0 $0 $0 N/A N/A N/A N/A N/A
Scenario 2 $49,692 $0 $806 $0 7% 30 12.4 0.0 9 Scenario 3 $49,334 $359 $3,106 $0 7% 30 12.4 1.4 8 Scenario 4 $48,616 $1,077 $3,648 $0 7% 30 12.4 3.7 6 Scenario 5 $47,988 $1,704 $6,307 $0 7% 30 12.4 3.4 7 Scenario 6 $32,516 $17,177 $12,000 $850 7% 30 12.4 16.9 1 Scenario 7 $32,516 $17,177 $12,806 $850 7% 30 12.4 15.8 2 Scenario 8 $32,485 $17,208 $15,106 $850 7% 30 12.4 13.4 3 Scenario 9 $32,423 $17,269 $15,648 $850 7% 30 12.4 13.0 4 Scenario 10 $32,369 $17,323 $18,307 $850 7% 30 12.4 11.2 5 Scenario 4 (Base case 2) $48,616 $0 $0 $0 N/A N/A N/A N/A N/A
Scenario 4a $47,964 $652 $8,100 ($597) 7% 30 12.4 1.9 1
Scenario 4b $47,898 $718 $17,550 ($1,743) 7% 30 12.4 1.7 2
Scenario 7 (Base case 3) $32,516 $0 $0 $0 N/A N/A N/A N/A N/A
Scenario 7a $32,470 $45 $8,100 ($597) 7% 30 12.4 1.0 2
Scenario 7b $32,361 $154 $16,550 ($1,743) 7% 30 12.4 1.4 1 1 Note that the estimated total risk of the base case is the existing risk, Re, and the estimated total risk of the alternatives is the modified risk, Rm. 2 Risk benefit is the difference between the existing risk, Re and the modified risk, Rm. 3 Initial costs, IC, and annual costs, AC, in the table indicate the cost difference from its respective base case; hence, when the required costs of alternatives
are less then the costs of its respective base case, negative costs may result (as shown in the brackets).
* N/A – Not applicable
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